main change by which domestic goats can be identified seems to be, as far as is known, of no economic importance. There is, of course, the possibility that it is linked genetically to other characteristics for which positive selection was taking place or it may be that billy goats can do less damage to one another when fighting if their horns are twisted; or it may be that they were easier to grasp when being caught; or maybe the early domesticators just preferred the horns that way (2) (3). l.i.i PRE-DISPOSITION of the GOAT for DOMESTICATION
It appears that a combination of several factors pre-disposed the goat to domestication.
The ability to survive on a diet high in cellulose and low in proteins, of which all bovids are capable, and to convert this material, otherwise of little direct use to man, into useful commodities such as milk, meat, hides, hair and wool, must have been a pre-adaptive factor in the successful domestication of bovids (4). Also, goats are relatively small, they breed regularly, have a short generation period, and are a social species which forms herds which can be easily handled by one man, especially with the aid of dogs (5) . The significance of the pre-adaptive role of' herd-behaviour' in domestication has been discussed by Reed (6). Goats are possibly the most versatile of all ruminants in their feeding habits, a factor which may have greatly influenced their success as a 4
domestic animal (3) . Also, the goat can provide the physical needs of clothing, meat, milk, as well as bone and sinew for artefacts, tallow for lighting and dung for fuel and manure to either the peasant farmer or the nomadic herdsman. "Goats will complement a flock of sheep, which are perhaps usually easier to herd, by browsing on thorny scrubland whilst the sheep prefer the grass. Goats may have been of positive assistance to the Neolithic farmers in helping to clear land after the primary forest was burnt or cut down." (3). l.ii LINEAGE of the DOMESTIC GOAT
Most researchers believe that the domestic goat, Capra hircus, derives from the 'wild goat', bezoar or pasang goat, Capra aegagrus (7), the only wild goat whose range extends from the lndus Valley westward through the Near East (Fig. 3.) (2), but, unfortunately, the term 'wild goats' is also applied to otherwild species of Capra (1). The range of C. aegagrus formerly extended into Greece and perhaps as far north as the Austrian Alps, and on Crete today some closely related examples of the wild ancestral strain still remain (2). Zoologically, the genus Capra is presently divided into six species
[Corbet (8) and Corbet and Hill (9), quoted by Mason(1)] :
-Capra aegagrus: the bezoar or wild goat.
-Capra ibex: : the ibex, with subspecies in the Alps, central Asia, the Near East and Ethiopia. Fig. 3. Distribution of wild goats. (From: Mason 1984, redrawn from Harris, 1962). I o o \
æ o È a t o ¿O ß a
ffi Markhor C. falconeri lbex C. ibex and h-l C. pyrenaica West Caucasian tur I C. caucasica East Caucasian tur mm C. cylindricornis N Tahr Hemitragus spp 0 1 000 2000 km 5
-Capra caucasica: the west Caucasian tur (Fig. 4.). This species has also been called the Kuban or west Caucasian ibex, C. ibex severtzovi.
-Capra cylindricornis: the tur of the eastern Caucasus (Fig. 5.). -Capra pyrenaica: the Spanish ibex or Spanish wild goat, with a national reserve in the Sierra de Gredos. -Capra falconeri: the markhor of Afghanistan, Pakistan and Tajikistan (Fig.6).
Although the name Capra hircus is still often applied to domestic goats, many zoologists prefer not to give species names to domestic animals at all. Some believe that if one has to refer to domestic goats by a scientific name, they should be called Capra aegagrus lorm hírcus, or, if some breeds are derived from the markhor, as has been suggested by some, these should be called Capra falconeri torm hircus (10). By contrast, Clutton-Brock (3) suggests a different classification scheme altogether, by which goats can be placed into four groups according to the shape and curvature of their horns, namely:
-Capra aegagrus: horn curved like a scimitar and the anterior surface is compressed laterally so as to form a sharp anterior keel. - Capra falconeri: horns that are twisted either as a straight screw or in an open spiral. The posterior of the horn is keeled but the front edge is usually flattened at least at its most proximal part (Fig. 6). -Capra ibex and Capra pyrenaica: untwisted scimitar-shaped horns as in the bezoar, but with anterior ridges or bosses over the full length of the horn. Fig.4. Capra caucasica; the west Gaucasian tur. (From Lydekker, R. 1898. Wild oxen, sheep and goats of all lands, living and extinct. Rowland Ward Ltd., London, facing page 246. 4
f= =ì
:,j Fig. 5. Capra cytindricornrs; the east Caucasian tur. (From Lydekker, R. 1898. Wild oxen, sheep and goats of all lands, living and extinct. Rowland Ward Ltd., London, facing page 243. ï:i,-1.1.,{}'Il.-t-rfrÌ\'.-i .LSïT Fig.6. Caprafalconeri: the markhor. (From Lydekker, R. 1898 Wild oxen, sheep and goats of all lands, living and extinct. Rowland Ward Ltd., London, facing page 286. ::;, :I'rl'.' --{ ì
Ë>.i.+it ]i;ilì lt Lli )j'i 6
-Capra cytindricornis : horns that are almost round in cross-section and which are curved in a single open spiral, and Capra caucasica wilh rather short widely-divergent horns (Figs. 4 &5). The chromosome number is known for only two of these groups of goats, the domestic goat, and the ibex, both of which have a diploid number of 60 (3). Corbett (8) accepts five subspecies of C. aegagrus, which has the anterior horn keel of domestic goats, the scimitar shape of which is mirrored in that of many modern breeds. "The bezoar sometimes has a slight twist at the end of the horn and it is presumably selection from this beginning that has given rise to the homonymously twisted horns of many modern breeds (i.e. with the right horn twisted clockwise)." "Animals with heteronymous horns (the right horn twisted anti-clockwise) are present in many Asiatic domestic breeds in the area between the Caucasus and Mongolia. These include the Kurdi of northern lraq, the down goats of Russian Central Asia and the cashmere goat of Mongolia (1)." Up to 1975 there was general agreement that the gene (or genes) for heteronymous twist was derived from the wild C.falconeri (markhor), suggesting that this was the ancient ancestor of these domestic breeds. lt seems that this could be due to more recent crossbreeding, however, as it has been shown that the domestic goat gives fertile offspring when crossed with the markhor (11). Dr. lan Smith (personal communication) has pointed out that horn shape can be changed in a single generation, as the horn type of the male domestic goat is dominant to that of the Himalayan lbex, for example (1). 7
i Alternatively, it has been suggested that heteronymous horns can exist as a variant within the C. aegagrus, as animals with heteronymous and with homonymous twists have been reported to occur in the same herd (1); but this is more likely to be due to intermittent crossbreeding of some of these animals with the markhor, (if these herds are located within the present-day range of this species), as this would be difficult to control, or prevent, in nomadic herds. Thus, the lineage of domestic goat species is still the subject of much debate. Whether the first domestic goats were descended from C.aegagrus or C.fatconeri, or both, very early in their history changes in morphology took place. Types were developed with lop ears, twisted horns, long hair and colours more varied than the wild animal. These must have were selected through the ages ü arisen as mutations which artificially qi I by the breeders. There is no evidence of association between climate or vegetation and hair length, ear length or coat colour either between or within breeds (1). "From this reserve of variation diffferent breeds or populations were developed which have beeri taken from place to place by migrant owners, crossed with other populations and selected for production of milk, meat and in some cases, wool. At the same time there has been a natural selection at work which has maintained or modified the adaptation of the goat to arid and mountainous environments" (1). I
I.i¡.i FIBRE PRODUCTION
Throughout recorded history the very diverse role of the goat has been appreciated. "Goats played an important role in the economy of ancient
Egypt. Their flesh was eaten., their skins were used to carry water and they were probably also milked'(1).
It is difficult to ascertain how long the goat coat has been used as a textile fibre by man, but "Greek and Roman writers record the prescence of fleece goats with fine fleeces in Phrygia and Gilicia (central
Anatolia) as early as the Sth century BC' (1). The value of goat fibre was already appreciated in early biblical times, as pointed out by Van der Westhuysen (12) in the following quote from the Old Testament:
ni "And the Lord saíd unto Moses: Thou shalt make cuftains of goats hair to 'ìE I be a covering upon the Tabernacle. Then Moses called unto him, from among the tribes of lsrael in the Desert of Sinai, the skilled spinners and weavers of fine goats hair to make the curtains as the Lord has commanded." Exodus 26
Today, two types of goat fibre are used as textile fibres: mohair and cashmere. Fibre production from these falls into two distinct industries, but both are speciality fibres (13). The fleece of the mohair-producing Angora goat "takes the form of a single coat of long, lustrous and curly fibres with a mean diameter of
I I i
! I
over 30!rm", usually without hairy fibres (1a). As with the Merino sheep li the tendency to moult has been lost (14). Cashmere fibre, on the other hand, is produced as the downy undercoat of a double fleeced goat (13). The cashmere goat can not be considered as a single type of animal. There are several varieties, rather than a distinct breed (13) (14). Almost all mammals which have hair coats grow an undercoat of varying degrees. In sheep of the primitive breeds, such as the Soay and the Mouflon (as in cashmere goats), this fine undercoat grows intermixed with the coarser outer coat to form a fleece of mixed-wool type. The undercoat develops during summer and autumn aS a secondary coat for winter warmth, and sheds during early spring. ln the improved breeds such as the pure Angora goat and the Merino sheep, this undercoat has reached its highest stage of development, making up the majority of the
ü fleece of almost continuously growing fibres. r,li I
I.¡i.ii CASHMERE GOATS
There is much confusion as to the specific lineage of the cashmere goat. As suggested earlier, its origin has been traced lo Capra falconerí by some authors, and to Capra aegagrus by others, and to three main domestication centres: North-East Kirgizia, South-West Tibet** and North-West Mongolia (Fig. 1) (15). ln view of this confusion over lineage
**Recorded as South-East Tibet in original reference; however, as pointed out by Dr. lan Smith there are no wild goats in the region of South-East Tibet nor are there any cashmere-producing domesticated I goats.
Ì 10
it seems more logical, at this point in time, to classify cashmere animals on the basis of performance, i.e. production of the fibre, rather than on Zoological origin (16). However, the animals originally referred to as the producers of the famous cashmere shawls were native to the Himalaya Mountain regions of Kashmir, lndia and China (17). Today, cashmere is commercially produced in Western China, Mongolia, Tibet, Northern lndia, lran, Afghanistan, the U.S.S.R., and more recently in Australia, New Zealand and Scotland.
I.iii CASHMERE FIBRE
Cashmere is an 'exotic' or'luxury' animal fibre which has for centuries been the basis of an international industry in fashion and luxury textiles animal fibres known to the ü (18). lt is one of the finest and softest 'I{& ,t textile industry (18). Cashmere garments are exceptionally soft and the fineness of the fibre enables the garments made from it to be very lightweight in relation to the level of thermal protection provided. These qualities have made it one of the most sought-after fibres for the finest, most expensive garments in the world. "Demand has always exceeded supply" (19). Cashmere is, however, not the finest of the exotic fibres. Musk-ox, ibex and vicuna fibres are all finer. The advantage, however, which cashmere
I production has traditionally had over the production of these other
exotic fibres is that it is produced by an animal which has been domesticated for meat and milk production for hundreds of years and t I I which is run in vast herds throughout the eastern world. Thus, the I
r 11
fibre has been available in significant quantities on a regular basis for quite some time.
The natural colour of the down can be white, grey, beige or tan, with the lighter shades bringing the highest prices, as these can be dyed pastel
shades (1 6).
Liii.i HISTORY of CASHMERE FIBRE
The story of cashmere dates back to at least the 15th century. Cashmere first became well-known for its use in the beautiful soft, light cashmere shawls, of exotic colours and intricate designs, for which lndia became famous (17) (19). "The most beautiful shawls were hand-woven in the city of Schrinigar, Kashmir, lndia, and it is said that at one time, Kashmir had 16,000 looms in constant work for these shawls" (16). These famous cashmere shawls of 150-200 years ago were so expensive, however, that only the royal families of Europe could afford them (16).
Cashmere garments are still 'speciality' or'luxury'garments, but today cashmere is used in such garments as sweaters, sports jackets and overcoats. However, because it is a soft, delicate fibre, fabrics made from it are not as durable as those made from wool (17). Europeans, and the French in particular, had such demand for the'exotic beauty'of the cashmere garments that they began importing cashmere goats into France in 1812, and by 1826 crosses of cashmere and angora goats had been made, producing a fibre which would now be called 'cashgora' (16). I
! 12
ln England, some of the original 1812 French imports were bought by a gentleman (C.T. Tower) of Essex, who established a herd which survived until at least the First World War. ln about 1828, another English herd was established by George lV at Windsor Park, using goats presented from the Essex herd. Then in '1889 Queen Victoria.introduced fresh blood into the Windsor herd by importing more goats from lndia. A third herd belonged to the
Duke of Buckingham at Stow Park (16) (20) . It seems, however, that none of these herds have survived. l.iii.ii DEF¡NlTlON of CASHMERE FIBRE
The word 'cashmere' is interchangeable with 'kazmir', 'pashmina' and 'casimi' by which names the fibre is more commonly known in its traditional areas of production (Dr. L Smith, personal communication) (16) (19). ' Pashm' is the Persian for wool and 'pashmina' means woollen.
Down is the name used in Russia (1). Many attempts have been made to define cashmere fibre. However, most researchers agree that all the current definitions for cashmere are, in fact, buying specifications and that no biological definition is available. Nor is there a biological definition which distinguishes the fibre called cashmere from mohair, or indeed from the fibre produced by cashmere-mohair crosses (21 ). A very general definition, however, is as follows:- "Cashmere is the very fine down or undercoat which grows under the 13
longer, coarser outer coat of a number of types of goats originally developed from wild goats in south-west Asia" (19).
l.iv AUSTRALIAN CASHMERE- HISTORICAL PERSPECTIVE
Liv.i Early Arrivals
ln the days of sailing ships it was common practice to take goats along on long voyages to provide milk and meat. They bred on board ship and the practice arose of putting surplus goats ashore on oceanic or offshore islands (22). Whilst historical records of the importation of goats into Australia are few and far between, it is generally accepted that early mariners introduced goats from many different countries into coastal Australia during the '17th century, either to offload surplus animals or as a result of shipwrecks. lt was possibly also done as a deliberate attempt to provide a source of food on offshore islands to aid future shipwrecked mariners (23) (24). This was apparently the case on a number of islands off the Queensland coast, particularly in the Whitsunday group, in the Recherche Archipelago in Western Australia, and probably in other places too (24). Goats were also introduced into the mainland of Australia by early settlers from the time of the First Fleet and throughout the 1800's; and almost certainly introductions were made from Asia and Africa by the early traders. " With the possible exception of the dog, no other 14
animal has been so intimately associated with pioneer settlements in Australia as the goat...... lt was taken as a domesticated animal to just about every corner of the continent (24) ." Lamond (25) points out that many outback babies survived only because the trusty old nanny supplied the milk to support their young lives. "The mob of 'town goats' is a legitimate part of Australian folklore, and many a story has been told about the town goats of Longreach or Bourke, Oodnadatta or Laverton" (23).
Goats were not only important in outback towns, however. They were found in almost every place in which man settled. They were used by miners, and road and rail construction gangs, boundary-fence riders, pastoral stations, overland telegraph stations, dogger's camps, and fishing villages, as a source of milk and meat, at a time when refrigeration was non-existent and transport was difficult (23). Throughout the world goats have a dual reputation, of being both useful and destructive. When found in large concentrations, they are infamous for landscape deterioration (23), and their reputation in Australia has been no exception to that elsewhere. The part played by the goat in destroying the natural vegetation is obvious from a letter written by a Port Augusta resident, South Australia, lo The Register in 1872: 15
" if ever a nuisance exists in any township in South Australia it does here. I believe that there are not less than 1,000 goats regularly fed around here, and camped every night in the streets and sheltered places. It is utterly impossible to either rest or to keep water because of them. Every corner stinks with them and the place is nothing else but a goat yard. While the Government derives a small revenue from them, are the powers that be aware that the goats are destroyíng every bush within four or five miles of the place, driving all horses away, and preventing all drays etc. from campíng near the place? " (26)
By 1880, an enormous quantity of sand had blown into St. Vincent's Gulf as a result of removal of trees for firewood and the browsing of the goats (26). "One of the many by-laws passed by the Corporation of Port Augusta in 1880 was devoted entirely to the goats. Any animal that now strayed in any part of the town did so at the risk of its life, and its owner was liable to a penalty of not less than 5s and not more than Ê1
(26).
However, the importation of goats had continued throughout the 19th Century with various acclimatization societies, whose specific aim was to import commercially useful exotic breeds, making specific importations of Angora, dairy and cashmere-type goats into Australia.
By the turn of the century considerable herds of Angora goats had built up and were thriving (27). ln 1862, in an anniversary speech to the society, an enthusiastic foundation member of the Victorian Acclimitization Society, Professor McOoy, is quoted as saying: 16
"Angora goats of Asia Minor we have introduced with great success and benefit, and in a few months we expect a large number of the pure Cashmere-shawl goat from Tibet, which have been already purchased for the society with the intention of forming a great herd on some of the highest mountains of Gipps Land which retain snow sufficiently long to produce the temperature necessary for preseruation of the fínest qualities of the wool and hair." (28)
It seems, however, that McOoy was an optimist, and the Angora goats to which he referred amounted to only seven, and were not of much benefit. Of the cashmere goats apparently few survived the sea journey, and those which did "wasted to death in the wet of Melbourne," as "it was found impracticable to get them to the dry cold country where McOoy pictured vast herds" (28). l.iv.ii AUSTRALIAN FERAL GOATS
Early goat herds in Australia were shepherded rather than fenced, so that when they were no longer needed, as a result of a declining demand for goat milk or meat, or because of livestock management difficulties, they were simply allowed to wander off. Town goats, for example were yarded at night but allowed tcj roam at will during the day. Thus, many goats escaped or were released into the bush following major changes such as the closure of mines e.g. Yudnamutna mines in the North Flinders
Ranges of South Australia or the closure of hotel stagecoach stops, e.g. 17
Mootwingee Hotel northeast of Broken Hill; and many of these animals reverted to the feral state (23) (24) (27) (29) (30) (31) (32). "Sources of feral goats, then, were numerous and varied (24). These animals carried with them, to the feral population, a variety of characteristics, including that, fortunately, of cashmere fibre production.
Hunting by man, and predation by dingoes and foxes, has affected the distribution of feral goats in Australia. Shelter is essential to limit the effects of predation; thus they avoid open grasslands. Also, as feral goats are dependent upon availability of drinking water, true desert environments are unfavourable. Thus, they have adapted to the drier, harsher conditons found in areas of low human population. ln some areas rough topography and dense vegetation have allowed goat populations to become established in agricultural areas (22). "The greatest density of feral goats is found in the Acacia shrubland (mulga) of Queensland, New South Wales, South and Western Australia
(23).' They are also found in the hilly terrain of the arid zone which has some shrub cover and a scattered herb layer. They also occur within the wheat and sheep, and high rainfall zones of southern and eastern Australia, where rough terrain and poorer soils are found (23), and are also located on some coastal islands (24) (29) (33).
The distribution of feral goats in Australia is shown in Fig. 7 (24). Feral goat numbers have been variably estimated to be between 200,000 and 2,000,000, an accurate determination of numbers being impossible due to seasonal variations (23) (24). Fig. 7. The di'stribution of feral goats in Australia
18
l.iv.iii THE DEVELOPMENT of an AUSTRALIAN CASHMERE INDUSTRY
The commercial exploitation of feral goats in Australia is only a recent development, considering these animals have been present since the early days of European settlement. Feral goats have been harvested for meat export since the early 1950's, regular abattoir slaughter of goats having commenced in 1952 (33) (37), and with the recession of the Australian wool industry in the early 1970's, the feral goat became the subject of increasing attention (27)- The realization that a ready export and domestic market existed for goat meat focused a number of speculative looks at the feral goats (32)' not only as a producer of meat, but also of leather and fibre. ln 1972, "during an examination of a small group of feral goats from western New South Wales, Dr. lan Smith of the University of Sydney, noticed a number of animals with profuse undercoats of soft, fine fibres
beneath their hairy outer coats. He took a fleece sample from one goat to Wal Clarke at the CSIRO Division of Animal Physiology in Sydney, who measured the characteristics of both the down and the hair" (31) (32)' At that time, Dr. G. Alexander, CSIRO, Prospect, had a small herd of feral does which he was using to study sheep/goat hybrids, and when Dr.
Smith approached Mr, Clarke at Prospect, they immediately examined Alexander's herd and found down on the does. Measured values confirmed that the goats were carrying cashmere fibre. Dr. Helen Newton-Turner of the CSIRO division of Animal Genetics and Mr. Fred Moylan of the Australian Mohair Company were shown samples '19
of the fibre and both expressed great interest. Mr. Moylan sent samples to two leading cashmere processors in Bradford, England, one of whom replied that they'd be delighted to take Australian cashmere if it were to become available in commercial quantities (31) (32) (35).
Also in 1972, at about the same time that cashmere was being
discovered on feral goats, Brian Thompson, a landowner of the Bathurst district of N.S.W., brought feral goats from the Wanaaring in Western N.S.W., for the purpose of eradicating blackberries on his property. The goats were an unselected group of about '1,000 does, bucks and kids. Later, other landowners did likewise (35).
ln 1974, the N.S.W. Department of Agriculture became interested in helping the Bathurst growers to upgrade the goats to produce cashmere (35).
"Through the efforts of lan Smith and Wal Clarke, a series of meetings were held in 1974-75 to discuss research aims and cashmere production. At that time a research project at Condobolin Research Station under Peter Holst was concentrating on meat production from
feral goats. Meanwhile, in the Tablelands of N.S.W., the interest in weed control by goats continued. The Bathurst landowner found that by 1976 his goats had controlled the weeds and a major culling programme was initiated. He retained 250 white does which formed the nucleus of the future flock of cashmere animals" (35). The number of people throughout Australia interested in cashmere production grew, until in January'1979 the Australian Cashmere Goat Society was formed, followed not long after by the Australian Cashmere 20
Goat Breeder's Society in mid 1980. At the same time various researchers within State Departments of Agriculture began observing and recording some aspects of the cashmere growth cycle and skin histology (36) (37) (38) (39) (40), whilst others began assessing the production potential of the feral goats and the value of selection and crossbreeding (34) þ1) (42) (43) (44). Yet other researchers turned their attention to the nutrition of the goat and the influence of this on fibre production (a5) Ø6) (47). Thus, in recent years, Australian feral goats have provided an excellent and quite unique opportunity for the development of a new rural industry with an estimated 10-30% of the animals carrying significantly useful quantities of cashmere (31) (19). As the feral population may be as high as 2 million it is an enormous genetic pool from which to select. As Couchman and O'Brien (19) point out, however, it is quite amazing that a population of down-producing goats should have survived or evolved among the feral goats of inland Australia, considering all previous attempts to produce cashmere, here and elsewhere, had failed. The evidence points to the fact that these earlier attempts may have been made in unsuitable climatic regions. However, given an opportunity to breed randomly in the wild, in regions which the goat finds most suitable, the goat has shown that it is indeed a survivor. 21
il FOLLICLE . FIBRE AND SEASONAL GROWTH lt.i HAIR
Superficially, hair distinguishes mammals from all other vertebrates. The forerunners of hair follicles Íìay, perhaps, have been the hair-like sensory appendages known as prototrichs, found in some amphibians and reptiles; but, whereas the feathers of birds are thought to have evolved from the scales of reptiles, hairs appear to have evolved in a position between those parts of the skin that in reptiles are covered by scales, i.e. the interscale region. Support for this theory comes from the observation that scales still exist on the tail in modern rodents, and that each scale has a row of three hairs behind it. Further evidence is provided by the fact that this trio arrangement of hairs is also still found in the skin in most mammals (48) (49) (50). Hair, or animal fibre, consists mainly of an insoluble protein, 'keratin'. Keratins are a group of highly specialized proteins produced in certain epithelial cells of higher vertebrates and they form the main bulk of the horny layer of the epidermis and of epidermal appendages such as hair, as already mentioned, and nails, claws, scales and feathers. Keratin-containing tissues are typically durable, pliable, insoluble, and relatively unreactive towards the natural environment. Thus, keratins would appear to have played an important part in the adaptation of
vertebrates to the rigours of life on land (51) (52). The epidermis itself , or "skin", is an extraordinary organ with numerous functions, one of the most important of which is that.it prevents the organism from I'
I 22 I t
whilst maintaining Ì dessicating and protects it from its environment, i ï communication with that environment (53). The epidermal appendages, i 1 j further protection to the organism. such as hair, add still '!; { å Thus, the fleece of sheep and goats, together with the skin, forms the i I i E protective covering of those animals, and sheep wool in particular, aided 3 r t perfection as by man's intervention over a thousand years, approaches ll q nature's cover for an animal which can face either the heat of Arabian f I deserts or the cold wet winters of the Welsh hills. The natural properties of these fibres of shedding rain and of insulating their wearers against variation in external temperature make them unequalled by any other fibres or materials, natural or man-made, for clothing (54). ln addition to its thermal proper:ties, the fleece works as a Sensory organ because of its close contact with the ne¡vous system of the skin (53). All hair follicles are surrounded by sensory nerves which react to pressure. "Highly specialized sensitive hairs (vibrissae) surround the eyes, lips and muzzle of all mammals except marì" (53). These vibrissae are particularly large in nocturnal mammals, and the follicles of these
I 'tactile' hairs abound in nerves (53). I As already mentioned in Part 1, the hairy coverings of a large number of animals are used to a greater or lesser extent as raw materials for the manufacture of different textile products. The principal fibre-producing animals are sheep, goats and camels, but the various species of sheep produce the bulk of fibres which are considered of any great economic importance. Under the term'wool', however, are included commercially 23 ì
I I 1
I I the fibres of the Angora goat, cashmere goat, camel, alpaca, llama, and vicuna (16). is an structure, As hair, or wool, is a product of the skin, it organized ll I composed of cells, which grows from the root, or follicle, situated in the t I I dermis, or lower layer of the skin. The follicle, therefore, is the unit of ¡ ,l fibre production. c 'I Thus, before the structure and production of animal fibres can be II i considered, follicle structure, the relationship of the follicle with the ¡ skin, and the way in which fibres are formed, all need to be understood
(55).
Most of the research on animal fibres has been carried out on sheep wool, human hair and rodent hair; therefore, the description of detailed structure, of both follicle and fibre, will be mainly confined to information gained from these. The general principles involved, however, are relevant to fibre production in all mammals, although minor variations exist between species. "The structural characteristics of hairs vary from one Species to another, from one region to another, and even within any given bodily area of the same animal" (53). í 24 I ' I rå il.¡¡ sKlN
rl ï in which hair follicles are .Þ Since the skin constitutes the environment i? I formed and grow, it is important, first of all, to briefly describe the Í I anatomy of the skin. ¿ I I The mammalian skin consists of two layers: an inner dermis and an outer epidermis from which follicles are formed. The epidermrs is divided into living and dead cell layers. The cornified uppermost layer of flattened dead cells, is made up of the stratum corneum and stratum lucidum. Cells of the stratum corneum are ì continually being worn away or shed. The living layer, or stratum malpighii, can be further subdivided into the granular (stratum granulosum), spinous (stratum spinosum) and basal (stratum germinativum) layers. The cells lost at the skin surface, are continually replaced by others which are produced by division of the cells in the lowest level of the epidermis, the basal layer (53) (56). This cell division is also important in the formation of the follicle. The dermis, which is much thiçker than the epidermis, extends down to the fat layer, panniculus adiposus, overlying the muscle layer or panniculus carnosus. The dermis consists of connective tissue which is made up mainly of collagen and elastic fibres (53) (56) (57). The layer of the dermis surrounding the follicles and skin glands is known as the papillary layer which is rich in blood vessels, nerves, and elastic fibres. Beneath the papillary layer is the reticular layer in which the collagen bundles are much larger and form a more open network; also blood 25
vessels, nerve fibres and elastic fibres are less frequent in this region
(57).
A hair follicle is a unique structure, in that it is an epidermal downgrowth in association with a dermal papilla (56). However, the structure of this unique arrangement is much more easily understood if follicle development, as it occurs in the fetus, is studied first.
II.iii FOLLICLE DEVELOPMENT
As stated earlier, follicles are formed from the epidermis by the same cell division in the basal layer which is responsible for replacing the epidermal cells lost by wear and tear at the epidermal surface. This cell division is not only responsible for epidermal replacement and the development of the follicle, however, but is also important in the growth of the fibre from the follicle (57). Although, in the middle of last century, it was first shown that animal fibres were arranged in characteristic groups in the skin, it was not until the 1930's that two types of follicle within the groups were recognized by Duerdin (58). The two types of follicle became known as Primary and Secondary follicles, and were fully described by Wildman and Carter (59). However, not all animals show both types; the elephant seal, for example,
has only one type of follicle (60).
Work by Carter (61) (62), Wildman and Carter (59), and Carter and Hardy (63) showed the main features of the arrangement of the follicles in the 26
i.
I
ì skin of sheep. Primary follicles each have a sweat (sudoriferous) gland, : I i an erector muscle and a sebaceous (wax or grease) gland (59) (61) (64) I I (65). Secondary follicles have only a sebaceous gland, but this may be I reduced or absent in some secondaries (57). ln sheep, the first follicles to form are the central primaries, followed later by two lateral primaries, one on each side of the central, thus forming the trio group (61). Lyne (56), however, points out that the central primary follicle primordia are not located at random with respect I I to one another, but are regularly spaced at least one diameter apad, and suggests that these first-formed follicles may act as 'organizers' of the lateral primary follicles which develop as'satellites'on either side. Later still the secondary follicles, which are usually more numerous than the primaries, develop within the areas between the central and lateral d lü ,l primaries (61). This trio arrangement of primary follicles has been found in most mammals studied. "ln some British breeds" (of sheep), "especially the New Zealand Romney and the N-type carpet-woolled strain derived from it, and also in the Mouflon, it has been noted that the primary
I follicles lie in distinct rows across the skin (57).' Although the trio group of primaries is that usually found, it is subject to variation, so that sometimes solitaries, couplets or tetra follicles are seen (57) (61). As a result of the different phases of follicle initiation, the final form of the follicle group is always simiiar in its spatial relationships. The lateral primaries lie slightly to one side of the central primary, on the outer (ectall side. lt follows that the secondary follicles also lie on
r 27
1l this side, the first formed secondaries on lhe ectal margin and the younger original secondaries in the middle of the group progressively toward the primaries (56) (57). To the opposite, or ental, side of the primaries lie the accessory structures. This is also the side to which the hair or wool fibre slopes. This arrangement is not standard in all mammals, however. Lyne (66) found that in the bandicoot the secondaries form on the ental side of the primaries. The primary trio with its associated secondary follicles constitutes the follicle group. The secondaries, being usually the smallest follicles, tend to grow finer fibres than the primaries; but the fundamental difference which distnguishes primaries from secondaries is the presence of the sweat gland and erector muscle. Carter and Hardy (63) showed that in the Merino sheep all primary rd iq follicles and a small proportion of secondary follicles had reached 'r maturity at birth. Hardy and Lyne (64) made further studies of follicle development in Merino sheep and showed that the majority of secondary follicles arise,
not directly from the epidermis, but as branches from the first secondary follicles. Thus, a distinction was drawn between original secondary follicles, which arise as buds from the epidermis, and derived secondary follicles, which are formed as buds from the original secondary follicles. The following description of individual follicle development, then, is relevant only to primary and original secondary follicle development. Derived secondary follicles will be discussed later.
I
r I I 28 I
ll.¡ii.i Development of the lndividual Follicle
Hardy (67) first suggested dividing follicle development into a series of
eight fundamental stages, based on studies of mouse follicle development. These stages were then expanded by Hardy and Lyne (64) (65), following studies on the Merino fetus, by dividing the second and third stages into two parts each, to make them applicable to other mammals. This was followed by a detailed study of follicle development in the human fetus by
Pinkus (68); and then a comparison of follicle development in the
ì bandicoot, possum, mouse, chinchilla, sheep and ox by Lyne (56). The first stage in the formation of a follicle is the multiplication of basal cells at a point in the epidermis, to produce a plug of cells. At the same time there is an aggregation of dermal cells beneath the plug. As a fr i{¡ result of further division this plug of epidermal cells grows down I cell into the dermis, usually at an oblique angle (57) (64). This was called the
follicle plug , or F1 stage by Hardy and Lyne (64) (65). Pinkus (68),
however, divides this stage into the prímitive hair germ or pre-germ , and the hair germ stages.
This first stage is followed by a down-growth, from its point of origin in the epidermis, of the hair germ into the dermis, in the shape of a solid column of epithelial cells which seems to push a cluster of mesodermal cells before it (57) (68). Simultaneously, an outgrowth appears on one I side of the developing follicle, which will later become the sebaceous gland. The follicles that are formed first (the primary follicles) have
T fr
r 29
tì
another outgrowth, which develops into a sweat gland, and which appears before the sebaceous gland. This is the pre-papilla or F2 stage described by Hardy and Lyne (64) (65), which for the primary follicles they divided
I into F2a to denote the appearance of the sweat gland rudiment, and F2b, I when the rudiment of the sebaceous gland is seen. Pinkus (68) called this the haír peg stage. The outer cells of the hair peg are columnar and arranged radially to the long axis; cells in the centre at first have no polarity, but later become arranged longitudinally. The advancing end is the broadest part of the peg and forms either a straight transverse plate I or is slightly concave because of pressure against the compact ball of I I
mesodermal cells, the future dermal papilla. The entire column is l mesodermal cells contiguous with those of the enveloped in a sheath of ! I i papilla (68). l As the follicle continues to grow longer, differentiation begins to occur. The advancing front enlarges, becomes bulbous and turns ín to form a dome-like structure, enveloping part of the mesodermal material which is then divided into the egg-shaped papilla inside the hollowed-out bulb of the matrix, and the papillary pad below the bulb. This third stage is referred to as lhe bulbous peg stage (68), F3 or papilla stage (64). At the same time, two solid epithelial swellings develop at the posterior side of the follicular column. The lower one only has been reported in the human fetus, and is inconspicuous in adult skin (68). "lt is a rounded knob the central cells of which soon accumulate lipid and appear foamy in
paraffin sections"...." This is a transient but regularly present fetal differentiation" (68).
{
I
I 30
,
t
I i
At a slightly later stage, the final permanent part of the pilary complex becomes visible. This is lhe arrector pili muscle. lt begins to form in the dermis at a little distance from the sebaceous gland. Mesodermal cells I arrange themselves into a narrow row, and gradually extend downward I
T toward the second and higher bulge, thus extending at an angle from the lower part of the follicle up to the epidermis. Also at this stage, a structure known as the hair canal begins to form in the epidermis. lt seems that there are differences in the formation of the hair canal in ditferent species. ln the sheep, the hair canals of both the primary and secondary follicles are formed by two separate processes; keratinization of epidermal cells followed by the appearance of an intercellular space, and at the same time an invasion of the follicle plug by sebaceous cells which then disintegrate to form spaces, resulting in a continuous canal running from the neck of the follicle to the upper part of the epidermis (6a) (69). However, in the mouse, no association between sebaceous cells and hair canal formation has been described (67); and in the human the hair canal was considered to be the continuation of the development of the follicle upward into the epidermis and not involving part of the epidermis (68). At this point of development all the components of the follicle are now present, and further stages are concerned only with growth and differentiation of these various parts. ln stage F4, (haír cone), the hair cone appears, being formed in the lower part of the follicle from elongated cells, often already keratinized, that will later form the outer (Henle) layer of the inner root sheath of the hair 31
a,
l
I1 fibre. At this stage too the sweat gland begins to form a lumen (57) (64).
By stage F5, the advanced hair cone stage, the hair cone has elongated to the level of the base of the sebaceous gland. Also, cells of what is to I I
T become the inner (Huxley) layer of the inner sheath of the fibre, and of the 1 I (57) (64). cuticle and cortex of the fibre, can be discerned within the cone t,
Eventually the fibre itself begins to form, in stage F6 (hair formation), : being produced by the multiplication of the epidermal cells around the i papilla, known as the matrix. The fibre and its inner sheath, made up I i eventually of three layers (Henle, Huxley and cuticle which interlocks I i with the cuticle of the fibre), grow up through the follicle together. The l :l
4 young fibre is pushed upward by the pressure from the dividing cells 1 I j below. By this stage the tip is keratinized, and therefore hard.
l ln stage F7 (hair in epidermis ), the tip of the fibre emerges from the inner sheath cone and enters the hair canal.
Finally, (stage F8- hair emerged ), the fibre breaks through the epidermis and appears above the skin surface; the cells of the original column that grew from the epidermis now become the outer sheath of the fibre (58) (64) (68)
Thus, all primary follicles, when fully differentiated, are associated with the accessory structures of an apocrine gland, an involuntary smooth muscle, and a sebaceous gland. ln contrast, the secondary follicle has only one accessory structure associated with it, the sebaceous gland, which may be reduced or even absent (57) (70). 32
As already mentioned, further follicles aríse as branches from the outer root sheath of the original follicles, usually at or above the sebaceous gland, but ocasionally below it, and they share a common orifice with their parent follicles (61) (65). Hardy and Lyne (65) referred to these clusters of follicles as follicle bundles, which is, of course, a smaller unit than the follicle group which refers to the basic unit of primaries, usually the trio group, and their associated secondaries. In the Merino, the first derived secondary follicle appears as a lateral bud on the original secondary at about the stage when the dermal papilla starts to form (61). ln the bandicoot the hair in the original follicle emerges before the branches appear, and these branches appear to remain stationary until the original follicle approaches the end of the first hair cycle (66). The derived follicles then develop rapidly and the original canal becomes the common hair canal for the follicle bundle (61) (66). ln most species studied so far,.branching is usually confined to the secondary follicles (64-66) (71-76\. However, Lyne (77) observed 'bundles' of primary follicles in the Merino, and also found that branching occurred in both the lateral primary follicles and the original secondary follicles in the marsupial, Trichosurus vullpecula (brush{ailed possum) (78). No branching was observed in the mouse (67) or the elephant seal (60). Branching has not been observed in cattle either, but the formation of paired follicles is common, whereby follicles form separate adjacent
epidermal primordia, but develop a common hair canal within the epidermis, emerging through a common orifice (79). The two follicles often form at different times and differ in size (79). i t I t I t 33 i :
I I
: \
i
¿ I I Bundles of hair follicles with a common orifice have been described in monotremes (75) (80), in marsupials (66) (81-83) and in eutherian i mammals (64) (65) (74) (76) (77) (79) (84) (85), but it is not clear as to I whether or not some of these are branched follicles or whether they simply share a common orifice through the epidermis. ll.iv FOLLICLE STRUCTURE
The follicle is thus a tubular structure, the wall of which is divided into two distinct layers, the inner and outer (root) sheaths. ll.iv.i The lnner Root Sheath
The inner root sheath is itself composed of three concentric layers, (as already mentioned briefly): Henle's layer, Huxley's layer and the cuticle. The first cells to show differentiation after ascending from the matrix
are those adjoining the inner surface of the glycogen-rich outer root sheath. The cells form trichohyalin granules while still within the bulbous part of the follicle and soon become keratinized at a low level in the follicle. These cells form Henle's layer, one cell in thickness, which rests against the outer root sheath and forms a rigid tubular sheath
around Huxley's layer, which is of variable thickness (57) (68). The
cuticle, or third layer of the inner root sheath, is composed of cells which interlock with those of the cuticle of the hair as the latter keratinizes.
These three layers grow up with the fibre from the follicle 34
bulb (57). Straile (86) suggested that the internal root sheath provides a strong link between the newly formed hair and the living cells of the external root sheath, until the hair is keratinized. Once keratinization occurs, and the link is no longer needed, the internal root sheath is abandoned by lytic action, and the fully developed hair is released from the follicle (86). ll.iv.ii The outer root sheath
The outer root sheath is the outer epithelial wall of the follicle and it extends from the epidermis to the dermal papilla. ln the region of the follicle above the opening of the sebaceous glands, the outer root sheath closely resembles the epidermis in structure; at lower levels it is mostly composed of basal cells arranged in more than one layer except around the bulb, where there is usually only one layer of cells (56).
For a long time, the outer sheath, or'trichilemma' as it was named by Pinkus (87), was thought to be an almost static structure continuous with the epidermis. However, it is now known that cell division does occur in this region, at least during the hair growth phase, and that trichilemmal cells move inward and upward and eventually keratinize and are shed into the neck of the follicle, just below the opening of the sebaceous duct, in the same way as dead cells are lost from the surface of the epidermis (86) (87) (88). Straile (88) suggested that in the mouse hair follicle, there was an upward flow of cells from the lower external root sheath during both anagen and catagen phases. 35
ì j I { I pointed observation from studies of human Pinkus (87) out an interesting ,l
I follicles, in that the outer root sheath does not keratinize as long as it is 't ; i covered with inner root sheath. lt only keratinizes in the follicular ',.' isthmus region of actively growing hairs, and in the sac surrounding hairs I'. I preparing to shed. In both cases, the inner root sheath has disappeared i (87). (86), observed that wherever the internal root sheath was Straile ; í dissolving or fragmenting, the adjacent cells of the external root sheath were hyalinized or flattened, and he considered that these cytologically altered cells may release lytic agents which break down the proteins of the internal root sheath. ll.iv.iii Connective Tissue Elements
The connective tissue elements of the hair follicle consist of the dermal papilla enclosed by the bulb, and the connective tissue sheath surrounding the hair follicle. At the light microscope level the connective tissue sheath is seen to be made up of a non-cellular layer and a cellular layer.
The first of these, the non-cellular layer, situated immediately outside the outer sheath, appears as a thin, homogeneous, vitreous, glassy, or hyaline/hyalin membrane under the light microscope (57) (Bg) (90) (91). This hyalin membrane varies in thickness in the ditferent regions of the follicle, being thick and conspicuous around the lower third of the follicle, but thin in the upper part (53) (90) (91). Electron microscope studies have shown that in the anagen follicle the
hyaline membrane consists of a basal lamina and two layers of :
il t 36 É I
,l
orthogonally arranged collagen fibres (90) (89) (92). The inner array of collagen fibrils adjoins the basal lamina of the cells of the outer root sheath and is orientated parallel to the long axis of the follicle. The outer arøy is oriented at right angles to the first (89) (53). A loosely arrayed layer of fibroblasts and macrophages surrounding the hyaline membrane consitutes the cellular part of the connective tissue l
: sheath, and is continuous with the papillary layer of the dermis (93) (90). *J { When stains are used it can be seen that there are many elastic t elastin ¡ ,{ fibres associated with these connective tissue sheaths, particularly in 't á I the region of the erector muscle attachment, and the elastic fibres often ì appear to continue into the epidermal outer sheath (57).
I i ì Mitotic divisions in the bulb give rise to the hair and inner root sheath. : i As the products ascend towards the skin surface they become elongated or flattened, and keratinized; and through mechanisms unknown are differentially converted into five or six dissimilar end products - Henle's layer, Huxley's layer, and cuticle of the inner root sheath, plus the cuticle, cortex and medulla (if present) of the fibre itself (94). Anatomically, the hair follicle can be divided into a permanent portion and a transient portion. The permanent portion is that part above, and including, the attachment of the arrector pili muscle; below this is the transient portion, the transient nature of which will be discussed in greater detail later. ln the upper follicle there is an open channel between the follicle wall and the hair shaft. ln the lower follicle the walls press closely on to the hair shaft (94). 37
; t ¡ f (I The lower, transient part of the follicle is probably best thought of as a ,1 4 I the sequence of 't series of functional zones, and from the base upward .: zones is as follows:- \
(a) The lower part of a fully-formed follicle is called the bulb and consists of a matrix of small, undifferentiated epidermis-derived cells which surround the dermal papilla. The dermal papilla is continuous with the connective tissue sheath. Mitotic activity takes place in the matrix cells and ceases at a point level with the tip of the dermal papilla' (b) Distally to the matrix is the zone of elongation in which the cells arrange themselves into columns and begin to elongate and differentiate. No mitotic activity is found in this region at all. (c) Above the elongation region is found the prekeratinization region, in which coarse and numerous fibrils are found within the cortical cells. (d) lmmediately above this is the keratogenous zone in which the cells are keratinized to form a recognizable hair (94-96) (53).
The permanent part of the follicle, above the insertion of the hair muscle, is best subdivided into the isthmus, and the pilosebaceous canal, its wall being formed by the pilosebaceous duct. The isthmus, below the duct, is narrow and in H & E stained sections looks rather uninteresting (97).
Pinkus (68) described it as a border zone peculiarly devoid of specific features. This isthmus, however, is a surprisingly interesting part of the follicle: it is endowed with nerve fibres which transmit the feeling that 38
the hair has been touched. lt is also provided with a dense coat of elastic fibres, which is much less prominent around the upper, pilosebaceous portion, and is normally almost completely absent from the lower, transient portion of the follicle (97). ll.v FIBRE STRUCTURE
Thus, the fully-formed fibre consists of an outer cuticle and an inner cortex. ln addition, particularly in coarser fibres, there is often a central portion, the medulla, which contains empty or gas-filled spaces. Each of these concentric parts is formed from separate streams of cells originating from the matrix. The cells of the cuticle, being flat, are known as scales, and overlap one another. The overlapping edges of the scales point toward the tip of the fibre and interlock with the similar cells of the inner root sheath (55). The relative proportions of the three components of fibre vary widely from one type of hair to another, and most coarse hairs contain a high proportion of medulla. In better quality wool and in cashmere fibre it is completely absent, and the cortex forms approximately 90% of the fibre
mass. The coarser types of wool, and in particular the so-called kemp wool, contains up to 15o/o of medulla cells which are many-sided in shape (e8).
A number of authors have described two thin additional layers inside and outside the cuticle of the fibre: the sub-cuticle (or endocuticle) and the
epicuticle. Whereas evidence for the existence of the sub-cuticle is 39
dwindling, the existence of an epicuticle seems to be well established. From the above, it will be clear that the epicuticle is not a cellular layer;
I it is either part of the main cuticle (which is the theory most favoured) ì
1 or a deposition on the surface. One possible source of deposition is the I inter-cellular material, often called cement substance, which originally : existed in the lower levels of the follicle between all the cells, and therefore between the cells of the fibre and the inner sheath (55). Much of the work on the detailed structure of keratin fibres has been carried out on wool because of its commercial importance. The cortical' cells in the fully formed fibre are not visible unless special treatments are used. One way of studying these cells is to attack the fibre mildly with a proteolytic enzyme such as trypsin, which breaks up the fibre into its constituent cells. An examination of individual cortical cells obtained in this way shows them to be much longer than they are wide and to have pointed ends. ln cross-section the cells are polygonal. Little work in this area seems to have been carried out on other fibres, but it has been shown that the cortical cells of camel hair are longer and more slender than those of sheep wool fibres (55).
ll.vi HAIR GROWTH CYCLE
Despite records of women with very long hair, and of unshorn sheep with several years'growth of wool, it is almost certain that no single hair grows continuously (99). Hair and wool growth occurs in cycles in which
periods of active growth alternate with periods of rest. Individual ,I
40
follicles sooner or later enter a resting stage, and moulting, or shedding, takes place at the end of this period (99). Although the bulb of a hair follicle is an epidermal derivative, its pattern of mitotic activity is strikingly different from that of the surface epidermis. While the rate of cell replacement in the surface epidermis is relatively steady, varying only within narrow limits according to diurnal and hormonal rhythms, the rate of cell production in the follicle is rhythmic, varying sharply between the violent mitotic activity associated with the formation of a new hair and the total lack of activity once that hair has been formed (9a). There appear, therefore, to be differences in physiological control between the mitotic activity of the surface epidermis and that of the growing follicle (94). There are three main phases in the hair growth cycle. The first stage is known as'Anagen', and is divided into follicle regeneration and active hair growth. The second, or intermediate stage is 'Catagen'which is the retrogressive stage. 'Telogen', the third stage, is the inactive, quiescent, or resting period (53) (56) (57) (93). ll.vi.i Anagen
The anagen follicle extends deep into the dermis where the bulb of mitotically active matrix cells produce the emerging hair.
Hair is a holocrine secretion, or exfoliate type of growth, arising from these matrix cells; the cells of the new tissue being removed at the same rate as they are produced (100) (96). 41
There are two major stages in the production of a hair fibre. ln the first, or proliferative phase, the cellular basis of the fibre components - cuticle, cortex and medulla (if present) - arc produced by the mitotic activity in the follicle.bulb and, as already pointed out, this mitotic activity is limited to the ectodermal component of the bulb - the matrix (94) (53) (101) (102). lt has been shown, however, that active mitosis only occurs when the epidermal cells are able to absorb adequate supplies of carbohydrate and of oxygen (94). ln the second, or'keratinization phase', the cellular mass produced in the bulb undergoes a series of complex physico-chemical changes in the lower regions of the follicle (57). Matrix cells have a characteristic ultrastructure with a spherical nucleus which occupies almost the entire cell, a scant cytoplasm with numerous ribosomes and some mitochondria and a few rough-surfaced endoplasmic reticulum. A compact Golgi zone is usually close to the nucleus, and some arrays of cisternae and vesicles make up the rest of the cell (53). As the cells move upwards they differentiate into the hair shaft, and the three layers of the inner root sheath (cuticle, Huxley's layer, Henle's layer). There is no mitotic activity in the region above the matrix at all (e4) (e5).
There is a close association between the number of cells produced per unit time in the follicle bulb and the rate of fibre growth (95). Schinckel (95) concluded that at least two-thirds of the differences in the rate of growth of fibre volume were due to differences in the number of cortical 42
1- ¡
it
¡
cells produced in the bulb. The remainder could be attributed to variations in volume of individual cells; that is, coarser fibres not only contain more cells than finer fibres but the cells themselves are somewhat larger (57) (94). However, he did not take into consideration differences in apportionment of cells between inner root sheath and fibre.
As Straile (86) has shown, a cellular shunt system exists which spatially determines which of the newly-formed cells will enter the hair and which will enter Huxley's layer of the internal root sheath. Straile (86) showed that in hair which changes shape throughout the seasons, such as rabbit or guinea pig hair, that in the transition from a round to a flat portion of hair, many of the bulb cells on two sides of the follicle are shunted into thick areas of Huxley's layer that complement, or'fill out', the depressed sides of the hair. ln other words, Huxley's layer acts as a depository for cells in excess of those required for the differentiation of the hair itself (86).
The anagen hair follicle produces hair continuously. According to Pinkus (88), matrix cells are produced and move up at a uniform speed of 0.3-0.4 mm per. day in the human follicle.
In anagen follicles, the dermal papilla is attached to a basal plate of connective tissue by a narrow stalk. Fibroblasts are the most numerous cells in the papillae and these fibroblasts also have the appearance of active cells with well-developed endoplasmic reticulum and Golgi complexes, and the cells are separated by connective tissue. A basement membrane separates the papilla from the cells of the bulb (53). 43
ll.vi.ii Catagen
Follicular activity comes to a halt gradually and in an orderly fashion through the catagen phase. Many of the structures of the growing follicles are eliminated as new structures of the resting follicle are formed. During catagen the entire lower part of the follicle, the cyclic or transient portion, undergoes complicated involutionary changes (103), and the telogen hair root moves up and comes to rest at the level of the bulge, i.e. the level of the attachment of the erector muscle, which remains the same length as in the growing fibre (53) (93). Here it is firmly anchored, (for approximately 3 months in the human), by the trichilemmal keratin forming the hard and dense hair club that one can see and feel on any fallen-out telogen hair. lts presênce is evidence of telogen effluvium (e4) (104). This shortening towards the skin surface is apparently brought about almost entirely by the orderly degeneration and shrinkage of the lower part of the follicle. Straile (88), presented evidence which suggested the possibility that active cellular movements in the lower external root sheath may be involved in the upward migration of the hair, club, and dermal papilla during catagen. He considered that although proliferation of external root sheath cells declines rapidly in early catagen, the cells may continue to move upward and slough into the pilary canal. Thus, decrease in size of the lower external root sheath may be largely due to
loss of cells at the zone of sloughing, rather than a degenerative loss
(88). 44
The newly-formed'club' or'brush-end' is believed to consist of modified cortical cells filled with non-oriented filaments. The brush is formed from the last few generations of cells to reach the keratinization region, I t germ 'l in less orderly streams than normal. Surrounding this club are the i cells, which are formed by the transformation, or degeneration, of the : outer root sheath cells during catagen. The inner sheath is lost late in catagen because it is possible to have a recognizable (yet incomplete) brush, with a normal inner root sheath. Once the club and the surrounding germ cells are formed, the follicle below them is completely resorbed, epithelial cells by cellular autophagy, the collagen fibres around the follicle by heterophagy (93). The onset of catagen is heralded by a loss of pigment in the fibre (53) (93) (96). The melanocytes, in the region of the tip of the dermal papilla cease the production of melanin, resorb their dendrites, and become indistinguishable from other matrix cells (96). Following this there is a decrease and finally a cessation of mitotic activity in the matrix cells. However, cells that are already partly differentiated continue to differentiate and migrate upward to form the last part of the hair shaft (53) (93), "consisting only of cortex and inner root sheath, until all that
remains of the bulb is a flimsy, disorganized column of cells" (53). The fibre narrows and ceases to produce a medulla (if it is a primary follicle). The cells in the lower part of the hair follicle begin to form large numbers of membrane-bound dense bodies, presumably lysosomes (91) Simultaneously, the plasma membranes of these cells undergo invagination and the basal lamina follows most of these infoldings (91). 45
Eventually the basal lamina becomes highly pleated and is finally completely resorbed. ln the dermal papilla at the onset of catagen, the basal lamina around the blood vessels invaginates into multiple layers. Also, the basal lamina that separates the papilla from the cells of the bulb becomes crinkled, possibly due to shrinking following the death and resorbtion of the endothelial and matrix cells, and the basal lamina is slowly resorbed. The rounded fibroblasts of the dermal papilla lose cytoplasm until their nucleus occupies most of the cells. Eventually these fibroblasts form a ball of cells with a neglibible amount of connective tissue between them and no blood vessels. Whether papilla cells decrease during catagen and then increase during the next anagen is not known: but they do not degenerate appreciably. lt seems that changes in the size of the papilla are mostly due to the increases and decreases in the size of the capillary plexus and intercellular substances (53). As might be expected, both the hyaline membrane and the connective tissue sheath undergo changes during catagen. The basal lamina undergoes extensive pleating tirat causes it to assume the shape of the thick, wrinkled sac seen under the light microscope (91) (53). During this characteristic pleating process the collagen fibres adjacent to the basal lamina become progressively disoriented and sandwiched in between the pleated basal lamina and the connective tissue sheath (90). At this stage, the cell population of the connective tissue sheath consists almost entirely of a tightly packed layer of macrophages, which Parakkal (90) suggested actively engulf and degrade the collagen fibres 46
immediately surrounding the follicle, which have already been partially broken down by collagenase. The cytoplasm of the macrophages are seen to contain engulfed collagen in various stages of degradation (90). Once within the cells, the collagen is completely broken down by hydrolytic enzymes. The macrophages show a polarity for collagen uptake, most of the membrane invaginations and phagocytic vesicles containing collagen being seen on the side of the cells facing the hair follicle (90). The bulb, and the papilla are not degenerate, but are dormant and eventually they give rise to a new hair to replace the old one.
ll.vi.iii Telogen
Once in telogen, follicles have achieved a mature, stable stage of il r.Þ quiescence (53). rf The telogen follicle has dual functions, and these are reflected in its structure (93). In such a follicle, two physiologically distinct regions can be easily discerned; one above the level of the sebaceous gland duct
i and the other below (9a). The cells in the upper region, in direct continuity with the surface epidermis, remain mitotically active like the epidermal cells. ln the lower region, the cells are mitotically inert (94). One function of the resting or telogen follicle is to hold in place the hair produced during the preceding anagen; the other function is to regenerate the next generation of anagen hair (93). The new structures which characterise the resting follicle are the club with the surrounding germ, and the dermal papilla which now looks like a
I 47
ball of cells underneath the germ (93). Between the brush and the bulb is the epithelial stalk which is indistinguishable from the undifferentiated plug of cells formed during development as a new follicle grows down from the epidermis (93). The club is responsible for anchoring the hair in position by means of keratinous rootlets situated between the germ cells of the epithelial sac (93) (53). The club cells are modified cortical cells filled with disoriented 80 A filaments. The germ cells give rise to the next generation of anagen hair. The germ cells are produced by the transformation of the outer root sheath cells at the middle level of the anagen follicle (93). Electron microscopy studies by Roth (105) of the telogen follicle in mice, showed that there are numerous desmosomal attachments between the ü !È l cuticle of the cortex and the external root sheath. The external root sheath has numerous intralayer desmosomes and basal attachment devices. Thus, the club hair is presumably firmly bound to the dermis. There is no internal root sheath in the telogen follicle. The three layers
of the hair are homologous to the corresponding fully keratinized layers in anagen. None of the cell organelles used for protein synthesis, protein secretion, or metabolism are identifiable in these layers. Telogen external root sheath cells are similar to external root sheath cells which are high in the anagen follicle. This layer increases in thickness and eventually keratinizes in a manner analogous to the epidermis. However, the granular endoplasmic reticulum and the Golgi regions are very
I inconspicuous in the telogen external root sheath. "Track-like" I
I
r 48
,1
arrangement of the collagen fibres, fibroblasts, vessels, and nerves parallel to the long axis of the hair was found in the dermis beneath the
follicle, and it was postulated by Roth (105) that this arrangement of the dermal elements, as well as the papilla, may aid in proper orientation of the next anagen hair.
ll.vi.iv Regeneration (Anagen once more)
The first stage in the regenerative phase of the anagen period is the elongation of the follicle bulb which grows downwards as a solid column of undifferentiated and dividing cells to surround the dermal papilla (53)' There is no mitotic activity in that part of the lower follicle which surrounds the brushlike base of the old hair. rd ltü and the tip ,l As the new follicle elongates rapidly, the inner follicle sheath of the newly forming hair begin to differentiate, and the cells involved cease to show mitosis.
Enlargement of the follicle continues as the new hair grows upwards alongside the brush of the old hair. lt is rare for an old hair to be shed from the follicle before the growth of a new one commences. In fact the growth of the new hair seems in some way to stimulate loss of the old one (53). The exact mechanism by which the old hair is released is unknown, but it
is thought to be more than mere mechanical stimulus. As a good diet is needed for regrowth of hair to take place, this explains
I why poor nutrition retards shedding (57).
I
r 49
ll.vi.v HAIR REPLACEMENT PATTERNS
There are three main types of hair growth cycle: Seasonal, Wave, and Mosaic. The most primitive cycle seems to be the'Seasonal'cycle in which animals have a visible moult either once a year (in spring) or twice ayear (spring/autumn). This occurs in many fur-bearing animals such as cats, dogs and rabbits, as well as in ungulates such as deer (106), horses (107), cattle (1OB) and wild and primitive breeds of sheep and goats (109) (57), although different species vary in the extent of the autumn moult. The second, or'Wave', cycle of hair replacement, iS seen in laboratory rats and mice. Hair replacement occurs as a band of activity, lasting two to three weeks, which passes along the body, the period of activity in { 'l less 1 month (57) (96). In this type of I each follicle being then
replacement, aS in seasonal moulting, adjacent follicles are in the same stage of the growth cycle at the same time. ln the third pattern of replacement, each follicle has its own cycle apparently independent of that of its neighbours. Hairs are replaced irregularly, so that the pattern of active and resting follicles has been described as a'Mosaic'. This type is found in the domestic guinea-pig and in man, and the active phase can last well over ayear. lt allows a constant length of coat to be maintained which is necessary, for example, in polar animals, and might also be found in tropical animals, which are not subject to seasonal changes in climate (57).
I
I
r 50
iì
It appears, however, that seasonal shedding may be superimposed upon the mosaic pattern as there are seasonal differences in the amount of hair shed, at least by humans, more being shed in autumn and spring (personal obseruation); although Pinkus (104) claims that at any one time in the
normal scalp, there are 80-85% of hairs in anagen ,1-2o/o in catagen, and
10-2Oo/" in telogen. Similarly, Kligman (110) claimed that on average, 13% (rang e 4-24) of follicles in the healthy human scalp are in telogen at any one time. ln animals which exhibit seasonal shedding, a long growing period alternates with usually a short resting period. However, those showing the wave type of fibre growth cycle, such as rats and mice, demonstrate relativley short periods (2-3 weeks) of hair growth and long resting periods which may last from weeks to several months (99). It has been suggested by Ryder (99), that moulting originated in lower animals, such as insects and reptiles, as a mechanism by which an animal with a rigid skin could grow. The shedding of the upper layer of the
epidermis, the stratum corneum, ¡s still retained in birds and mammals,
but is a continuous process barely visible as such tiny fragments are shed. ln whales, however, the stratum corneum is lost in large sheets and occurs at six-monthly intervals, similar to hair moulting in some mammals (99). Similarly the southern elephant seal sheds sheets of stratum corneum attached to the club hairs, as the latter shed (60). This can occur either as small patches or large sheets and the size, which indicates the rate of
{t 51
shedding, may be dependent upon latitude and/or temperature (J.K. Ling - personal communication). Moulting in the southern elephant seal is an annual event occuring in spring (60). Thus, the main function of moulting in higher animals appears to be the disposal and replacement of worn-out skin strucfes (99); and this replacement of feathers and hairs is also a means of providing the animal with different coats for summer and winter, i.e. in preparation for changes in ambient temperature (99) (57). ll.vi.vi SEASONAL CHANGES lN COAT
Many mammalian species exhibit seasonal changes in their pelage, the usual pattern being the production of dense, fine fibre which traps warm air for winter warmth, and a less dense coat in the spring and summer through which air easily circulates, allowing evaporative cooling. Sometimes, however, in hot arid regions thermoneutrality is maintained by having a thick coat in summer which prevents heat gain from the environment. For example, in the red kangaroo (Megaleia rufa), which inhabits open country, the average dorsal hair density in summer is 62lmm, whereas in the euro or hill kangaroo (Macropus robustus), which spends hot summer days in the shelter of caves and rocks, has a much
lower density of 19.Zlmm (1 1 1).
Cycles of fibre production and shedding, have been well documented in the
sheep (57) (1 12) (113) (1 17-130), Mouflon, or wild sheep (109) (131), goat (132) (133), cattle (107) (108) (134-136), whitetailed deer (137), i. i 52 f
Ì1 I I
red deer (106) (138) (139) (140), Asian wild ass (141), domestic horse (142) (143), southern elephant seal (60) (144) (145), Weddell seal (146), Cape fur seal (147), grey seal (148) (149), silver fox (150) (151), coyote (152), cat (153), Barrow ground squirrel (154), weasel (155), ferret (156) (157), mink (158) (159) (160) (161-163), stoat (164) (165), short- and long-tailed weasel (166) (167), pocket gopher (168), Indian horse-shoe bat (169), bent-winged bat (170), varying hare (171), snowshoe hare (172), mountain hare (173), cottontail rabbil(174),wild rabbit (175),
I muskrat (176), otter (177), cotton rat (178), shrew (179), mole (180), and ìl meadow mouse (181). I a
i "ln the hair cycle variations may occur in the initiation of acivity, which .1 determines both the timing of the molt and how many hairs grow; in the duration of anagen and the rate of production of hair, which determine the amount of hair grown; and in the loss or retention of club hairs, which affects the density of the coat" (182). As stated earlier, some animals such as the ass (141), wild pony (184), silver fox (151), cattle (134), wild sheep (131) and goats (132) (133)
have a visible moult only once ayeat, with the shedding of the heavy winter coat in spring and the gradual growth of a new winter coat throughout the summer. Others moult twice a year and grow hairs with different characteristics at different times, and often a change of colour is involved, for example from brown to white. The field vole, for example, has many more hairs per unit of skin area in winter compared to those in summer, the increase being due mainly to an increase in the
number of fine underhairs. Also, all the hairs are finer. This increase in 53
density is acheived by more hajr follicles becoming active at the autumn moult than at the spring moult, and fewer resting club hairs being lost in the autumn than in the spring and summer (182) (184). However, in some animals in which only a spring moult is visible, e.g. some ruminants, a l
proportion of the outer hairs is replaced at the end of summer too, I J ì ¡ although their shedding is not obvious (195); and in some, e.g. the ,t I !t Wiltshire Horn, it was claimed that the subsidiary shedding cycles in I primary (121). I summer involved the secondary as well as the fibres i Pelage and molting in wild mammals, with special reference to aquatic forms was comprehensively reviewed by Ling in 1970 (186). The majority of the studies quoted, however, were merely observations made of the externally visible moult, without histological data to support these observations. As pointed out by Ling (186), "only careful studies at the follicular level can resolve unequivocally questions of duration and frequency of molt". It is now widely accepted that seasonal variation in wool growth in many domestic breeds of sheep is a modified vestige of the primitive rhythm of moulting and replacement of fibres (57). The more primitive breeds of sheep such as the Mouflon (57) (109), Shetland (187), Soay (119) (123) (188) and Wiltshire Horn (121) (189), shed their woolly undercoat completely every spring. Other breeds vary in their degree of shedding- The double-coated hills breeds such as the Scottish Blackface (190) and Herdwick (112), for example, shed approximately 60% of their secondary fibres in spring, whilst the Shropshire Down breed shed as much as 84/o (54). Other breeds show considerably less seasonal shedding, such as 54
10/"in the Devon Longwool and only 4/"in the Cheviot (54), and the incidence of shedding was never found to exceedlo/o of all fibres in
Merinos examined by Ryder (191). Lyne (1 18), however, found as much as 8.5/" of fibres (primary and secondary) shedding in one Merino and 12.1"/o in a Southdown-Merino crossbred animal. It must be remembered, however, that these figures represent measurements taken from the mid-side position from a small number of animals, and are probably not representative of the whole body let alone of the whole breed.
Even where shedding is not evident there is a reduction in wool growth during autumn and winter in most sheep breeds (192) (193) (194) (195), which was thought initially to be due to poor nutrition at that time of year. lt has been shown, however, that even when animals are kept on a constant plane of nutrition wool growth is still reduced during winter (192) (193) (196) (197), thus supporting the theory that this variation in wool growth rate is an evolutionary remnant of the once adaptively useful mechanism of shedding.
ll.vii CONTROLLING MECHANISMS OF FIBRE GROWTH CYCLES
Ebling and Johnson (198) (199) on the basis of skin-grafting experiments in rats, suggested that there were two controlling factors in follicular activity. First, there is an inherent rhythm possibly involving the build-up of an inhibitor in the follicle itself, which would stop cell :
i I 55 I t I ,¡ I I
i
!
ì I i division when the concentration reached a certain level; and second, there is a systemic factor (probably hormonal). lt was suggested that the inherent rhythm is normally subject to the systemic factor(s). The inherent rhythm of transposed autografts was apparently also found in haired- and woolled-skin on black Merinos (200). Unfortunately immunological barriers prevent further work on cross-over skin-grafting between different sheep breeds, e.g. those which shed with those which do not.
It seems reasonable to assume that environmental changes in some way bring about seasonal changes in fibre production. ln the natural environment various factors tend to vary together from season to season, and it seems likely that these changes act together to influence the seasonal changes of coat. Much scientific research has been designed to examine factors in isolation from one another in order to determine the role of each. The possibility of nutritional influence upon variations in wool production has already been briefly mentioned. That poor grazing results in low fleece weight has been known for some time, and abundant food stimulates increased wool production (100) (201) (202). In the Soay it was obserued that shedding in ewes was later than that in rams, and it was suggested that the nutritional drain of lactation was responsible for this, assuming that shedding of the old fleece is dependent upon growth of the new (113). Slee (203) also found an association between level of nutrition and shedding of the birthcoat in Wiltshire lambs; those which gained weight most rapidly shed first. Also, voles on a higher plane of l
I 56 t t l
I I i I I
I
I I nutrition moult earlier than those on a low plane (204). Poor nutrition has also been shown to delay moulting in Caribou and in grey seals (186). Other environmental influences have also been suggested as causes of change in fibre production, such as shearing. Although Downes and Lyne (205) found no increase in production as a result of shearing, Wodzicka (206) found that animals shorn monthly grew more wool than those shorn at six-monthly intervals. A possible reason for this is that food intake was increased, after shearing in cold weather, in response to increased maintenance requirements, and that the increase in food consumption may in turn have had an effect upon wool production. Temperature changes too have been suggested as a possible influence on fibre production. Coop and Hart (207) found no change in wool production in winter in sheep exposed to an increase in temperature of 7o C. Similarly, Hutchinson and Wodzicka-Tomaszewska (208) quote some work in the Canadian winter in which sheep were given a temperature increase of as much as 29" F with no increase in wool production. However, when Wodzicka (206) subjected sheep to constant short-days there was no change in the seasonal pattern of wool production, the greatest production still being in summer, therefore it was concluded that temperature was the controlling factor. Other workers, however, have concluded that this lack of immediate response to altered day-length is in fact due to an inherent rhythm, which is already attuned to natural day-length (209) (210), and which may
persist for up to two years following reversal of normal lighting 57
regimes, but that after this time the wool growth rhythm changes to coincide with the new regime, regardless of temperature remaining unaltered (210).. This was confirmed by exposing sheep to winter temperatures of 40o C and reducing summer temperatures lo 20" C whilst normal seasonal lighting was maintained. No obvious change in the wool
j growth cycle was observed. Morris (210) concluded that the seasonal 'ì 1 wool growth cycle is induced by seasonal day-length changes.
] Watson (173) and Jackes and Watson (211) thought that moulting in hares was retarded by low temperature and snow-lie but Ryder (132) suggested 1
* "The persistence of the wool growth rhythm for some time after the supposed stimuli had been changed, or removed, as observed by Morris and earlier workers, is in keeping with observations in other animals. The so-called "biological-clock" associated with these internal rhythms has been studied mainly in connexion with 24-h rhythms, and the interpretation has been that rhythms persist after the stimuli have been removed because they are firmly imprinted on the animal. The relationship of the stimulus to the internal "clock" is considered to be of the nature of a resetting of the "clock" to coincide with the external rhythm. Thus the internal clock can continue to act for some time in the absence of external stimuli, but if the external stimuli begin to occur at a different time the intenal clock will gradually adjust itself to come into line with the changed conditions" (57). 5B
that low nutrition could equally well cause the delay. Temperature has , been shown to be a modifying factor in the seasonal change of pelage in ! I weasels which moult more slowly when kept under cold rather than warm '. i conditions (167). Although moulting in the stoat appeared to be related to temperature stoats exposed to warmer conditions than normal took longer to moult, and the moult was prevented completely in one animal (164) (165). lt has been suggested, however, that temperature has an indirect effect upon pelage changes in that it brings about a change in behaviour of the animal. ln colder weather animals such as stoats and weasels spend more time sleeping and thus by their behaviour curtail their own exposure to daylight. ln warmer conditions the reverse is true (165). As early as 1935 Bissonnette (212) showed that the pelage cycles in the ferret were related to daylength. These, and further studies by Bissonnette (213) and Harvey and MacFarlane (156), established that there is a correlation between the sexual cycle and the hair cycle in relation to daylength. As daylength increases ferrets come into oestrus and grow summer coats; with decreasing daylength they enter anoestrus and grow winter coats. Such a correlation between increasing daylength and induction of spring-type pelage, and association of autumn-type pelage with decreasing daylength has also been shown in shrews (214), weasels (166), mink (158,159), varying hare (171), cattle (134,135), red deer (140), and silver fox (150,151). From studies of photoperiodic effect on sheep, indirect evidence has been provided that decreasing daylength in autumn provides the stimulus which suppresses wool follicle activity, to the point at which they may 59
1 even enter the winter rest period; and that increasing daylength in spring I is the stimulus that reactivates the follicles. The resulting new growth of wool is presumed in turn to stimulate the moult (or casting) of the old coat (1 14) (1 1 5) (1 17) (185) (193-197). Rougeot (1 14) found that anoestrus and wool follicle activity began 1-2 weeks after the longest day. The timing of the moult can therefore be modified in many animals by manipulating the photoperiod. For example, voles kept on long days in autumn grow summer coats with a low density of hairs and coarse guard hair, whereas short days in summer stimulate the growth of a dense, fine winter coat (215). Artificially extended daylength in winter advances both the onset of oestrus and shedding in the mare (143). Similarly, long days in winter advances the spring pelage change and subsequent rut and autumn pelage change in the white-tailed buck (216), and also advances the spring moult in the roe deer (217). Exposure of red deer to a daylength cycle of six months duration doubled the frequency of the coat change, and the stags grew antlers twice a year (140). The Soay sheep moults earlier if subjected to long days during winter, whereas short days during summer advance the onset of winter follicular inactivity (188), and Morris (210) has shown that a reversal of daylength between summer and winter will eventually result in a complete reversal of the seasonal rhythm of wool growth, although it may take up to two years for the biological clock to readjust. Hart (218,219) showed that if sheep were hooded to block the light stimulus the seasonal rhythm of wool growth was virtually eliminated. He also suggested that differences ''
I 60 i ì ñ ;l j in light intensity act in the same way as contrasts of light and dark, as he I observed no difference between sheep kept on continuous light by giving I them artificial light of only 5ft candles (approx. 55 lux) after dark, and animals which experienced solar light only (219). This theory of the importance of light intensity was supported by Hutchinson (220) who showed that wool growth rhythm can be suppressed by exposure of sheep to a continuous low intensity of illumination. ll.vii.i HORMONAL INFLUENCE
"Although direct effects of light on tissues cannot be excluded, the effects of light are probably indirect and mediated via photoreceptors which transduce the incident light energy to signals transmitted over neural or neural-endocrine pathways to target tissues" (200). Bullough (221) and Bullough and Laurence (94) extensively reviewed the control of mitotic activity in mañrmalian epidermal tissues, and the role of hormones in cell growth and differentiation. Bullough (221) suggested that hormones may influence but not control mitosis, the control factor being located in the tissues themselves. He suggested that hormones which stimulate or inhibit such mitotic activity are tissue-specific
rather than mitosis-specific. As cells of most tissues are capable of indefinite growth, Bullough suggested that control must be exercised through an anti-mitotic factor which acts together with less local hormonal mechanisms to control cell division (221). Such a factor has been demonstated and has been called a chalone (94). 61
However, "a permanent innate systemic timing factor seems improbable in long growth cycles, and unnecessary in seasonal cycles, which seem to be linked to external seasonal changes." (57) Slee and Carter (129) suggested various possible systems of control of the shedding of the different fibre types of sheep. They postulated (a) innate systemic control, (b) innate local control by the follicle in which the fibre grew to a fixed length, or for a fixed time, which would explain the shedding of kemps at times other than the main moult, and (c) environmental control. lnnate systemic and local control could be determined by the genotype. At least three endocrine glands influence wool growth by the secretion of hormones; the anterior pituitary, the thyroid and the adrenal cortex. Ferguson (222) suggested three possible types of hormonal influence. Firstly, the permissive role of hormone secretions, necessary for wool growth to take place but which do not affect the rate of growth. Secondly, the regulatory role in which variations in secretion rate control the level of wool production, and probably shedding. Thirdly, a pharmacological effect when hormones are administered artificially in greater amounts than those in the normal secretion. 62
ll.vii.i.i Pineal Gland
There is now a great deal of evidence that the pineal functions as a mediator for light-induced seasonal rhythms in several species with regard to pelage changes (223) (224) (225), as well as changes in body weight (223), and antler growth (2J25)'. Houssay, Pazo and Epper (226) showed that removal of the pineal accelerated the hair growth waves in male mice. When bilateral ganglionectomy, considered to have the same effect as pinealectomy, as it destroys the sympathetic inneruation to the head, was performed on mink, it was found that this rendered mink unresponsive to the artificial manipulation of daylength (224). This confirmed the data of Murphy and James (227), on mink, and that of Renfree et al (228) on a marsupial. Ganglionectomy, however, did not alter the moult in animals left under natural conditions (224). Martinet and Allain (224) thought that this may
be explained if the function of the pineal is only to synchronize endogenous rhythms with the natural daylength variation. Ganglionectomy
altered the timing of the events, but did not change the events themselves.
ll.vii.i.ii Pituitary Gland
The direct involvement of the pituitary gland in the photoperiodic control of the moulting cycle was first demontrated by Bissonnette (213) who showed that hypophysectomy prevented moulting in ferrets. Further work by Lyman (171) showed that when whole sheep pituitaries were fed to 63
Varying hares the white winter coat changed to a brown summer coat. More recent work has shown that hypophysectomy also prevents moulting in mink (224) (229), weasels (230) and white-tailed deer (225)- Experiments with the short-tailed weasel showed that the hormone responsible for this coat colour change is melanocyte-stimulating hormone (MSH) (230). After hypophysectomy in the weasel, the hair growth induced by plucking results in the establishment of a winter-type pelage regardless of whether the coat was white (winter) or brown (summer) at the time of the operation (230). Hypophysectomized weasels treated with melanocyte-stimulating hormone (MSH) or corticotrophin (ACTH) grew pigmented summer-type hair after growth-initiation by plucking the white hair; hypophysectomized controls, however, grew white hair after plucking and did not moult (230). Similar results were found for hypophysectomized mink, but in those which were hypophysectomized whilst in summer pelage asynchronous shedding occurred after the winter pelage was induced by plucking, and the animals died, probably from an inability to withstand winter cold (229). Rust and Meyer (231) induced pelage colour changes and moulting, as well as testicular changes, in melatonin treated weasels held in 14 hours light and 10 hours dark (long days). They showed also that when brown summer hair was plucked in order to stimulate new growth, it was replaced by white winter hair in treated animals which then shed their coats and grew another white coat. Other melatonin treated animals shed their white coats, replacing them with coats of the same colour despite the 64
long photoperiod of 14 hrs light. Also, initiation of hair growth was retarded in melatonin-treated animals. They suggested that pineal gland melatonin caused the release of an inhibiting factor to MSH by the hypothalamus, thus preventing the release of MSH by the pituitary. Hoffman (232) found that for hamsters kept in short photoperiods there was no difference between controls and melatonin-treated animals. But coat colour change was accelerated by exposure of winter animals to long photoperiods, and this acceleration was delayed by melatonin. Thus, it is generally assumed that the daily rhythm of melatonin secretion conveys information about daylength to the neuroendocrine axis (224) (233). Work by Martinet, Allain and Weiner (234), suggested a direct role for changing prolactin concentrations in the induction of the autumn moult in mink. Exposure of animals to short days or treatment with bromocriptine both decreased prolactin concentration, and in turn resulted in a brief moult showing characteristics of the winter gradient, i.e. progressing from tail to head and leading to dense winter pelage. This suggests that decrease in plasma prolaetin induced by decreasing daylength through the mediation of melatonin is responsible for the autumn moult and growth of
the winter coat. Duncan and Goldman (235) arrived at similar conclusion based on studies of pelage changes in the Djungarian hamster; injection of bromocriptine stimulated the winter moult in hamsters housed in long photoperiods. Goldman (233) showed that daily injections of melatonin one hour before 65
lights-off mimicked and strengthened the inhibitory effect of short days on prolactin secretion and consequently on luteal eell and hair follicle activity. Although it appears certain that prolactin is involved in the hair follicle activity cycle, its mechanism of action remains unknown. The pituitary is, of course, the "master" gland of the endocrine system, and some of its hormones act by stimulating other endocrine glands. Two of these are the thyrotrophic hormone which controls the secretion of thyroxine by the thyroid, and adrenocorticotrophic hormone (ACTH) which acts on the adrenal cortex. ll.vii.i.iii Thyroid Gland
Removal of the thyroid gland from newborn lambs prevents the maturation of follicles, and in adults reduces wool growth to about half the normal rate (236). Injections of thyroxine restored normal growth rate (236).
However, it has been shown that thyroxine does not restore activity to inactive follicles (237). This reduction in wool growth is not merely due to a loss of appetite, and it seems that throxine has a regulat ory as well as a permissive role in the control of wool growth (238). Administration of thyroxine to sheep with an intact thyroid stimulates wool growth; however, it also stimulates increased heart rate, respiration rate and body temperature (239) (240). Feed intake is increased too but not sufficiently to compensate for body changes and animals tend to lose weight. 66
Rougeot (241) found that thyroxirfinfluences wool growth by changing the cell size and increases fibre length but not diameter. lt does not alter mitotic activity. Lyman (171) observed no histological differences in thyroid activity in varying hares at differing stages of the moult and concluded that the thyroid did not influence pelage changes in this species. Similarly, treatment with thyrotropin failed to induce moulting in hypophysectomized weasels and mink, and the administration of thyroxin did not have any affect on pelage growth in these species (229) (230). However, Reinecke eTal (242) showed that thyroid gland destruction inhibited the spring moult in mink, but the animals went through an autumn moult and grew a winter coat, although of poor quality. This was followed by a normal spring moult after the administration of thyroprotein in the diel(242). Experiments with the field vole suggest that it is the increased output of thyroid hormone in spring which both initiates the moult and leads to the growth of coarse hairs (243\.
ll.vii.i.iv. Adrenal Cortex
ln contrast to pituitary and thyroid hormones, the major effect of hormones of the adrenal cortex is of slowing wool growth. Daily injections of ACTH slow down growth by decreasing both diameter and length, and in extreme cases wool growth is stopped altogether (57). Similarly, injection of sheep with cortisone slows wool growth (57). 67
Disease, cold, injury and extremely poor nutrition are known to cause stresses which stimulate the adrenal cortex, and this may be the main way in which these conditions affect wool growth (57). Downes and
Wallace (244) however, found that it was only larger dose rates of cortisol which depress wool growth, and that smaller doses actually increase the rate. Two Varying hares were maintained in brown and white pelage by the administration of adrenocortical extracts, initiation of growth of a new coat apparently being prevented (171).
Also, moulting and replacement of fur was accelerated in adrenalectomized mink (229), and plucked areas of skin on short-tailed weasels regrew brown pelage after hypophysectomy followed by administration of adrenocorticotropin or MSH (230). I{ From these experiments it appears that ACTH may inhibit hair growth and ,r pelage change altogether, or at least inhibit all but the spring-type moult to dark pelage or promote melanogenesis. Epidermal mitosis is inhibited by hormones of the adrenal cortex (221), and the general inhibitory effect of the adrenals on hair growth has been shown in rats and mice (245) (246).
Similarly, adrenal hormones have been implicated in the hair loss which occurs under a variety of stress conditions in humans (110).
þ 68
1 ll.vii.i.v Gonads
Whilst diffuse hair loss in the postparturient woman has been a well-known clinical fact for some time, Lynfield (247) showed that this was probably due to a return to the normal cycle of hormones after pregnancy. Her findings indicated that during pregnancy the conversion of hair from anagen to telogen is slowed down, and postpartum the conversion from anagen to telogen is accelerated; (although an alternate possibility is that pregnancy is associated with a more rapid shedding of telogen hairs, so that fewer were found in samples throughout pregnancy).
It is not clear, however, which hormone or combination of hormones is responsible. However, Mohn (245) showed that, in the rat, estrogens prolong the anagen phase once a cycle has begun. Harvey and Macfarlane (156) found that hair growth and shedding in ferrets was not inhibited by [t $ rf oestrogen. Lyman (171) found no retardation or acceleration of pelage changes in gonadectomized Varying hares exposed to different light regimes, but
found there was a heavier moult in these animals, indicating that
I gonadectomy promotes hair growth. The pelage cycle of intact and hypophysectomized mink, however, was unaffected by administration of gonadotropins, and gonadectomy did not influece hair growth in any way
(22e). Hypophysectomized weasels treated with unfractionated ovine gonadotropin moulted and grew white winter pelage, but when hypophysectomized animals were given gonadotropin plus ACTH, they
I grew the brown summer palge after moulting (230). Thus, there appears
I
Ì 69
to be a mutual interaction between the adrenals and gonads leading to a spring-type moult to brown, whereas the gonads alone appear to either promote the growth of white wihter pelage or suppress the brown summer coat (232). Experiments to determine the effect of female sex hormones, used to fatten animals, upon wool growth in sheep found that oestradiol and to a lesser extent diethylstilboestrol, reduced wool production by decreasing length of fibres, but had no effect upon diameter (248). Draper et al (249), however, found that wool growth was reduced only when food was also restricted. The effects of progesterone are variable. ln mice, spontaneous hair replacement is inhibited by progesterone (246) (250); but in ferrets hair growth and shedding were stimulated by progesterone treatment (156). I ü rrù Leutotropin did not effect hair growth in weasels or mink (229) (230). I Hair growth in the human can be classed as androgen-independent or androgen-dependent (251 ). Androgen-dependent hair consists of axillary and pubic hair, and face, trunk and extremity hair. In both men and women, normal axillary and pubic hair growth is dependent only on adrenal or ovarian androgen (251) (252). However, a normal male androgen (testosterone) plasma level is essential for the development of for the development of I hairs of the face, chest, and extremities, and
: coarse body hairs; however the enzyme Scr-reductase, which converts I L testosterone to dihydrotestosterone, must also be present as well as a specific androgen receptor in the hair follicle. Hair follicles from normal
T from regions of androgen-dependent or I adult men and women, whether
I
Ì 70
-independent hair growth, all have similar capacities to form dihydrotestosterone from testosterone (251 ). However, a significantly higher Scr-reductase activity was found in frontal regions of balding men
than in hairs from the frontal regions of nonbalding men and women (252). i' Both anagen and telogen hair roots contain the same androgen enzymatic systems, but in telogen hairs fewer metabolites were found (252). Khateeb and Johnson (243) carried out experiments in the vole aimed at isolating the effects of various hormones and suggested that although thyroid hormone in spring initiates the moult and leads to the growth of coarse hairs, at the same time, the increased output of sex hormones inhibits hair growth so that fewer hairs grow; castration in spring results in a dense coat like the winter coat. The increase in adrenal cortical hormones encourages loss of club hairs. The result is a sparse pelage with coarse hairs. The autumn moult occurs when the endocrine glands are regressing. Thus, a reduced amount of sex hormone allows more hairs to grow; keeping voles on long days in autumn maintains the size of the gonads and leads to the growth of a sparse coat like the summer coat. Lower levels of adrenal hormones may result in retention of resting club hairs; treatment with ACTH in autumn encourages loss of club hairs. The lowered secretion of thyroid hormone results in fine hairs;
administration of thyroxine in autumn to voles kept on short days results
in the growth of hairs of winter density but summer coarseness. The normal autumn changes result in a dense pelage with fine hairs (243). 71
All of this evidence makes it reasonable to conclude that the seasonal changes of coat are adjusted to the environment by way of the endocrine system. However, the determinants of hair growth are multiple and there is apparently a complex interaction between them. The moult cycle in wild mammals appears to be geared to the activity cycles of the gonads, thyroid and adrenal glands, and is influenced by a changing output of MSH in mammals with a seasonal colour change.
ll.viii SKIN HISTOLOGY and FIBRE POPULAT¡ONS of GOATS
Although the cashmere industry dates back hundreds of years, there is very little information on the production of the fibre at the animal level, let alone at the follicle level. This is not surprising when most of the world's cashmere production emanates from nomadic tribesmen and peasant farmers in Asiatic countries.
Very little, in fact, has been written even on skin histology or fibre characteristics of Angora goats. However, Margolena (253) examined skin biopsies and hair from both North American and South African Angora
does and found that despite decades of survival and selective breeding in
the different countries and different hemispheres, it was ditficult to
distinguish between skin biopsies of corresponding age with respect to follicle density, disposition of follicles and the incidence and size of sebaceous glands. The typical trio of primary follicles was found and S/P ratios varied from 6.10-10.00 (253).
I 72
Dreyer and Marincowitz (254) found that in the South African Angora goats which they studied, the primary follicles were arranged in an arc with the secondaries opposite. Secondary follicles were usually organized in short rows of three to four follicles each. Branching of .
secondary fibres shared a : follicles was not obserued but often several 1
l common orifice. S/P ratio was similar to those studied by previous '¡ I I authors, i.e. 8.70-9.40 at two years of age, with no significant difference ,-l l between males and females (254). Preliminary studies (253) of fleece samples and skin specimens from Australian Angora goats from thre'e states showed that, with respect to S/P ratio (7.50-8.80), mean diameter and percentage medullation, they were similar to the North American and South African animals studied by Margolena (255). Following crossbreeding of imported Angora and indigenous Gaddi goats in lndia, aimed at evolvíng a suitable breed which would combine both mohair quality and hardiness for sub-Himalayan areas, Pant and Kapri (256) studied the hair follicle ratios of both parents and offspring, with a view to selecting goats on the basis of hair follicle ratios for future breeding. Secondary follicles in the Gaddi were found to be almost non-existent, having an S/P ratio of 0.0187, whereas the Angoras had an S/P ratio of 6.56. Their crosses, however, showed a tendency towards high S/P ratio, that of the first crosses averaging 5.58, which increased to 6.25 in the F2 generation (256). The skin of some other breeds'of goats, other than the Angora, have received sporadic attention, for various reasons. 73
Burns (257), in a study primarily designed to find a means of selecting breeding stock to produce superior skins for the leather trade, made a histological study of the skin of the Red Sokoto, (the skin of which is used for Morocco leather), the Brown Kano of Nigeria, and some goats from Bulasso of undefined breed. lt was found that the secondary follicles, although quite numero.us were extremely small, both in diameter and length, and the majority lay above, or only just within, the level of the primary sebaceous glands (257). Also, above the level of the sudoriferous gland ducts there was fusion of the root sheaths of secondary follicles, usually in pairs, but occasionally three or four fibres became enclosed in a common orifice (257). A similar arrangement was found in the common American goat (258). ln all the goats studied by Burns, the S/P ratio was found to be approximately 4.00 (257). Burns also found that although the tendency for the secondaries to lie between the primary follicles was often manifest, it was by no means universal. ln addition, the relative positions of primaries and secondaries were different at different skin levels, the bulbs of the secondaries tending to lie more in line with the primaries, whilst the distal parts of the secondaries tended to occupy a more ectal position (257). This observation is similar to that found in woolled sheep. No information was obtained on the hair cycle in these goats (257); her interest centered mainly on the leather qualities rather than on the growth and development of the hair or fleece cover. Margolena (259) described the development of the skin glands and follicle population of the common American and Toggenburg goats to find out i
I i
I 74 i
whether essential differences existed between these and the Karakul sheep. lt was determined that in both types of goat, as indeed in the Karakul, the larger primary follicles remain distinguishable throughout their lives but that differences in size between the primary and secondary follicles was more pronounced in the goats (259). lt was also found that the hair of both the goats and the Karakul develop in follicles that are more or less slanting throughout their pre- and post-natal histories, unlike the twisted and curled follicles of the Merino sheep. The Karakul and goats were also similar in that the primary hair pierces the skin before or at 120 days of uterine life. The main difference found between the Karakul sheep and the goats, however, was in the initiation and development of the secondary follicles. ln the Karakul initiation of the secondaries is practically confined to a few weeks and keratinization is close to completion a few days before birth, whereas in both types of goat initiation extended from about 135 days of fetal life to the first postnatal month.
It was concluded that goats are more like fine wool sheep than the Karakul in this respect (259). lt was also found that follicle bulbs of goats attain their mature dimensions later in development than those of the Karakul. S/P ratio of these dairy goats was found to be 3.97 (range e-14) (25e). Sar and Calhoun (258) made a thorough and detailed study of all components of the skin of the common American goat and reported the usual trio group of primary follicles with which were associated from three to six secondaries (S/P ratio 1.00-2.00). They reported 'compound I I
I ì I
75 I I
secondary follicles', but it is not clear whether these were 'branched' follicles or fibres arising from a common orifice; and the bulbs of the secondary follicles were located higher in the dermis than those of the primaries (258).
Ryder (260) described the follicle group in two specimens of domestic goat, one Nigerian and one British, and found that the skin was similar to both those of the hairy domestic sheep and of the Barbary sheep. A study of two populations of Scottish goats by Ryder (133) showed that these animals had widely-spaced follicle groups compared with most domestic sheep, with central primaries much larger than the laterals, and the two first formed secondaries distinguished from those formed later by their larger size. The seconlaries formed two wedges in the gaps between the central and the lateral primaries, and the first secondaries to be formed lay at the base of these wedges (133). This finding is similar to that for Angora animals (254), Saanen-type animals with Angora influence and milch-type goats (132), in which the secondary follicles containing the largest fibres are situated furthest from the primary group, whereas the smallest fibres are located nearest the primary site. S/P ratio was found to be significantly different between the two groups of Scottish goats, one averaging 3.75 and the other 4.39 (133). Also, Ryder found that these goats completely lacked underfur (down) in the summer (261). lt is not clear when the fine fibres commenced growth as fibres were measured only twice; once in winter and once in summer (133). 76
t I
Similarly, Ryder found that Scottish milch goats (S/P ratio = 4.00) and
Australian Saanen-type with Angora influence (S/P ratio = 6.00) were without secondary fibres for most of the summer months as the old wool tended to be lost before growth of the new was evident (in late summer) (132). The primary fibres formed brush ends at about the time of the autumn equinox and remained dormant until late spring, and the majority of both secondary and primary follicles became active immediately after the longest day (132). There was no evidence of more than one peak of primary follicle shedding as had been noted in Scottish Blackface (190), Masham (196), Mouflon (109) and Limousin sheep (114), (132).
ll.viii.i SKIN HISTOLOGY and FIBRE of CASHMERE-TYPE GOATS
Until the well-known study by Burns, Von Bergen and Young (18), no detailed study of cashmere fibre, as related to the coat of the animal, had been published. Burns et al (18) not only reviewed and co-ordinated the physical characteristics of cashmere, compared percentages of, and fineness of down from animals from different countries, they also eliminated much of the confusion concerning its origin and characteristics, by bringing together conflicting information from different sources in an attempt to clarify the meaning of "cashmere". Discussions relating to the definition of the fibre, however, have continued. During their investigation, they also analysed some entire fleeces of 77
some lranian and Afghani goats. They also pointed out that even by then (1962), the Russians had "bred up their down-producing goats to a high individual production unequalled elsewhere in the world" (18). Burns et al (18) distinguished three coat types; the cashmere type, the intermediate type and the common goat hair type. The microscopic structure of the fibre, was reported as being like merino wool, consisting (18). of the epidermis and cortical layer, and without a medulla I Following this study, the only other major work relating to cashmere animals was, until recently, that carried out in the U.S.S.R., and very little of the information reached the western world. Summaries of some of the studies have, however, appeared in Animal Breeding Abstracts and have been collated by Barrie Restall, Senior Research Scientist at the Wollongbar Agricultural Research Centre, N.S.W. (unpublished data). He points out, however, that some caution is needed in interpreting the data as the information abstracted may be highly selective due to limited access to U.S.S.R. reports by the abstractors; and that it is possible that errors may have arisen in translation; for example, the words mohair/down and hair/ kemp are frequently interchanged.
1n 1973 the first reports of cashmere-bearing Australian feral goats were published (31) (32). Smith and Clarke (32) pointed out that many breeds of goat have an undercoat of fine fibres interspersed with the coarse hair. "The proportion of down in the fleece varies from nil in
Spanish goats lo 75o/" by weight in unsorted Chinese cashmere fleeces; only in the fleece of goats maintained for cashmere and down production
does the amount usually exceed 507o" (32). As some of the feral goats 78
which they examined carried up to 87"/" down fibre, with a mean diameter of only 13.5 microns, clearly this could be considered cashmere (32)' The Australian goat population at that time could easily be divided into three breeds, or types - Angora, milking, and feral - and Clarke (261) made a preliminary comparison of the fibre and follicle characteristics of these three different types in order to establish some basic biological data of the follicle populations of Australian goats (261). S/P ratios were found to be approximately 3.70 for the milking breeds, 5.80-7.00 for the ferals and 6.40-9.10 for the Angoras (261). Holst (33), in a survey of over 500 feral goats sent to abbatoirs from two different regions of New South Wales, found that white was the predominant colour in these particular Australian feral goat herds and that hair length varied significantly between the two areas. lt was suggested that these differences in hair length could have been due to differences in ancestry, but that they were more likely due to sampling at different times of the year, one group being measured in autumn and the other in spring (33). These reports were followed by further studies of the potential of cashmere-bearing feral goats by Holst et al (36) and Couchman and McGregor (37). Holst et al (36) found similar S/P ratio values to those of Clarke (261), i.e. 6.10, and found that in does located at latitude 33 degrees South, maximum cashmere length was obtained in May and moulting occurred from July to September. Couchman and McGregor (37) investigated 93 feral, F1 and F2 79
cashmere-producing goats in order to establish baseline production data for Australian down-bearing goats. They examined total fibre, down yield, fibre diameter, grease and moisture content and found that yield and fleece characteristics compared favourably with those of traditional cashmere-producing countries, the yield varying from 117-1319 for females and 153-1659 for males, in the combined F1 and F2 generations. They also concluded that visual assessment was reliable for on-farm selection (37). At Wolongbar Research Centre an unselected herd of feral does of mixed age and colour, which had kidded at various times of the year, was studied for fleece characteristics (27). Down production varied from less than one gram lo 212 grams with an average of 499, and mean diameter was 15.4pm. Mean S/P ratio was 5.80, ranging from 2.50-10.28. lt was found that both pregnancy and lactation reduced down production with lactation having the greatest effect. Does which kidded in April and were therefore both pregnant and lactating during the down growing season, produced only half the down of does not kidding at all (27'¡. Analysis of the various components of down production using fleece, skin and body weight data showed that variation in length and cover were the most important sources of variation in down weight (27). Phenotypic correlations
between components of down weight showed strong positive relationships between length, diameter, cover, and down weþht, but negative relationships between cover, density and body weight. This suggested that selection for down weight would result in an increase in diameter,
length and cover in the flock. However, if attention was also 80
paid to body weight, the increase in density would not be achieved (27). Fleece measurements carried out on the18 month old progeny from random matings of the unselected feral herd showed an increase in average down production to 88.9 grams (27). More recently, reports of cashmere characteristics and production have come from some lndian studieS. Acharya and Sharma (262) described the production and quality of pashmina in the Ghangthangi breed of goat, one of the two Indian breeds identified as producing cashmere fibre. The other breed is the Chegu (262). Although they found the lndian cashmere to be superior to that from other countries in terms of fineness (mean diameter 13.36-13.58), they suggested that there was scope for improving production per animal (262'). Yields per animals were found to be similar to those from Australian feral goats, but much lower than those from Soviet breeds and thus it was suggested that the Changthangi be crossed with Soviet goats, especially the Don, which has an average pashmina production of B00g per year (262).
The hair follicle and fibre characteristics of both Chegu and Changthangi goats was reported by Koul et al (263). They found no difference between
breeds with regard to S/P ratio or follicle density, but found differences
between sexes, females having significantly higher secondary follicle density (42.40 and 38.56) than males (27.10 and 29.67). Density of primary follicles was also higher in females but not significantly so (263). lt is possible that differences in body size may have accounted for these differences in follicle density; however, this was not suggested by the authors. Female goats also had finer fibres (12.06-12.12pm vs. 81
13.04-13.64pm) in all regions of the body and cashmere length was also significantly lower in females (41.47mm vs. 53.35mm) (263). S/P ratio ranged from 5.78 to 7.60 which is similar to that in Australian cashmere goats (261), (263). Follicle density of lndian goats (263), however, was found to be higher than that of Australian goats (36). One of the most interesting fibre producing goats which has been reported recently is the Zhongwei fur goat of northwest China (264). Adult males and females carry 240 and 170 grams, respectively, of undercoat fibre which makes up approximately 87.50% of the total fleece, and has a mean fibre diameter of only 1 4.17¡tm and an average stretched length o17.2 cm. The newborn kid is completely covered with pure white curly staples about 4.00 cm long which reach 7.00 cm at about 35 days of age, "when they form beautiful crimpy strands. At this time the kid is usually slaughtered for its fur" (264). lt was found that these goats adapted well when moved to less harsh climatic areas and were found to mate earlier in the warmer provinces. The crossing of two breeds of native goats with the introduced Zhongwei sires significantly improved fibre quality in the
F1 and F2 generations (264). The interest in possible new areas of production of cashmere fibre turned some attention to the undercoat of feral goats in other countries too, such as Britain (20) (265) (266) and New Zealand (266) (267) (268). New Zealand, by 1988, was already producing more than 10 tonne and it is estimated that Britain could produce 50 tonne of cashmere from up to one million goats (266). +". l' 82 I t
¿ l
111 THESIS OBJECTIVES
When I began this thesis, in late 1982, the Australian cashmere industry was relatively new and producers were hungry for information which might aid them in their selection and management procedures. Thus, my overall aim in approaching the research work for this thesis was to gain some fundamental information about the production of cashmere fibre at the individual level which would be of use to the farmerlproducer in his/her management strategies.
It appeared to me that, before any complex experimental research is to
be carried out it was, first of all, necessary to determine the existing pattern of production of cashmere fibre from Australian animals, such as determining the exact length of the growing season and the age at which secondary follicles are fully matured in the young animal. Only when these existing patterns'are established is it possible to determine the effects of changes in environment, hormone levels, reproductive status, management strategies etc. upon these established patterns.
Thus, to this end I sought to investigate the seasonal pattern of fibre production in adult animals; the study of secondary follicle development in young animals born at different times of the year, and the effect of pregnancy and lactation upon production of the fibre. The results of some of these investigations led me to further investigate some aspects in more detail. Since 1982 results of work from several Australian research centres
has appeared in press, some of which, as will be seen later, complement
the work presented here. I
Ghapter n
Postnata[ Dcvc[ópmnent of Seeondary Fo[[üo[cs f,n Austna[ilan @ashnncnc
Goat Ktds" 83
1.1 ABSTRACT
Development of secondary hair follicles was studied in three sets of twin goat kids, from two weeks to fourteen months of age, in order to determine the age at which full cashmere production potential has been reached. Kids achieved maximum secondary follicle development (determined from monthly skin secondary to primary follicle tS/Pl ratio measurements) at about 20 weeks after birth, at which time cashmere percentage, determined from fibre samples, was found to be a good approximation of the proportion of secondary follicles of these animals born in October (spring). No difference ¡n S/P ratio or rate of secondary follicle maturity was found between male and female kids.
It is proposed that S/P ratio determinations on skin biposy samples would not be significantly more useful than fibre diameter measurements taken at the same time. lf S/P ratio measurements
are to be made, samples should be taken during the summer months when the follicles are act¡ve, in order to avoid difficulties encountered with such measurements during the resting or shedding stage. Fibre diameter was greatest during summer, narrowing again in winter immediately before shedding.
It is suggested that fibre samples taken between the ages of 20 and 40 weeks of age may be used to select animals for production purposes, at least for kids born in spring. 84
1.2 INTRODUCTION:
Studies of follicle development in the sheep fetus have determined that primary follicles are formed first, secondary follicles being formed later (56) (61) (64) (65) . Schinckel (269), however, pointed out that it was necessary, when discussi ng'follicle development', to distinguish between follicles which have begun to develop but which have not attained the final phase of fibre production, and mature follicles which are producing a fibre. Follicle development can thus be considered to occur in two stages, i.e. initiation (physical development of the follicle) and maturation (production of fibre from the follicle). Although all secondary follicles are initiated before birth, many do not mature, i.e. do not produce fibres, until after b¡rth. Assessment of production potential from the secondary follicle may be made in two ways. lt may be expressed as a ratio of secondary to primary follicles, i.e. the S/P ratio, or it may be expressed as density of follicles per unit area of skin. S/P ratio, however, is often a more appropriate measure to use, as no allowance need be made for skin expansion as the animal grows, i.e. when measuring in kids or lambs, nor for shrinkage of skin during processing. Thus, S/P ratio has been used extensively as a means of measuring secondary follicle maturation after b¡rth (269) (270), and also to compare sheep breeds one to the other (62) (271) (54). For instance, it is now well established that in the Merino all primary follicles are mature at birth (118) (270), and all, or 85
almost all, secondary follicles are'initiated' before birth (272). Wildman (273), however, showed that this is not so in other breeds. He found that in the British Romney not all follicles are initiated before birth, and also that follicles may regress during the first week after birth. Lyne (1 18) has suggested that, in the Merino, most of the immature follicles seen at birth and in early postnatal samples are derived secändaries, which arise from branching either from the original secondary or from other derived secondaries. The age at which all secondary follicle development is complete also appears to vary between different breeds of sheep, but all continue to undergo secondary follicle maturation after birth. Burns found that development was complete by 1 month in the Herdwick (112),6 weeks in the Sutfolk (274), and 3 months in the Scottish Blackface (190) and the Romney (275). Fraser (270) and Schinckel (269) showed that in the Australian Merino all secondary follicles were productive at about 17-18 weeks of age, although the majority
had reached maturity by about 3 weeks, with the greatest increase in S/P ratio occurring in the 2nd week after birth, or between 12-18 days (270). ln the New Zealand Romney the period of peak development of new secondaries is between 20 and 24 days (276). As sheep and goats are closely related species it seems reasonable to assume that goats would similarly show continued maturation of secondary follicles after birth. lndeed, this was found to be true of Angora goats, as studied by Dreyer and Marincowitz (254). 86
They showed that secondary follicle maturation continued until the age of six months, with the greatest increase in S/P ratio occuring within the first three months after birth. Lambert et al (39),
) however, consider that in the Australian feral goat postnatal I follicle development involves not only maturation but initiation too. I I f Again in sheep, it has been shown that nutrition has an important ¡ I 'II influence on the development and/or maturation of the secondary follicle population. Although reports have disagreed as to the precise'critical time'of this nutritional influence on development of the follicle, there appears to be no doubt that poor nutrition in early life does lead to decreased mature fibre production. Turner (277) showed that nutritionally-handicapped lambs (twins and lambs from maiden, two-toothed ewes), showed a reduced S/P ratio
ü later in life. Fraser (270) suggested that sensitivity to nutritional lü tî deficit is probably restricted to some early phase in the differentiation of the follicle, and since the first visible differentiation of a secondary follicle occurs at about 20-30 days before its development of a wool fibre, at least in the Merino, then the period over which nutritional level will be most likely to be important is from 30 days before birth to 35 days after birth. Schinckel (269) suggested that poor nutrition before birth may prevent the initiation of some secondary follicle anlage. By contrast, Short e7e) e72) found that pre-natal nutrition had no effect on the initiation of secondary follicles and suggested that lr early post-natal nutrition exerted most influence over mature
þ 87
secondary follicle population. Results of studies by Schinckel and Short (279) contradicted those of Turner (277 -see above) in that they found that poor nutrition in the young !amb, i.e. after birth, d¡d not permanently affect the number of follicles, i.e. the mature S/P
ratio, but that it did reduce the volume of fibre produced and hence total wool production. ln other words poor nutrition in early life may permanently affect the'efficiency' of the follicles, i.e. their metabolic ability to convert raw materials into fibre keratins (279). ln a nutritional study with goats, Lambert et al (39) found that nutritional supplementation during the last month of pregnancy and the first month after birth had little effect on adult follicle population. However, supplementation during early pregnancy was associated with a significant increase in density of secondary follicles at one month of age (39). dr€ I Since nutrition appears to be so important during the developmental period of secondary follicles it is important, therefore, to determine precisely when this development is taking place, since the manipulation of the level of nutrition for this short period could have a marked effect upon adult fibre production. This is particularly important when the commercially valuable fibre, such as cashmere, is produced only by the secondary follicles and not by the primaries.
I Moreover, as it is the aim of most producers to select animals for I breeding and/or production at an early age, it is important to
T I
I
r 88
determine the age at which full production potential has been reached or can be gauged. The aim of this experiment, then, was to determine the age at which all secondary follicles have reached maturity in cashmere-type feral goat kids.
1.3 MATERIALS and METHODS
1.3.1 Animals
Three sets of twin kids, each set comprising one male and one female, and born within two days of one another, were chosen for the purposes of this experiment and ear-tagged for easy ü ,J identification. These animals were the offspring of unselected 'bred-on' feral does, the parents of which were feral animals
captured in the Flinders' Ranges of South Australia, and taken to the Mortlock Experimental Station, Mintaro, South Australia, three years previously, to form the nucleus of a goat-meat experimental program.
Kids remained with their mothers and ran with the rest of the herd, at Mintaro, until 3 months of age when they were weaned ( the
I normal weaning age). They were then moved to the Waite Agricultural Research lnstitute, but continued to have no special treatment, being subject only to usual farm practices and run on
I i
Ì 89
normal pasture, with supplementary feeding when necessary. Male kids were not castrated, but left entire. Unfortunately, one kid died in March, 1982, approximately one third of the way through the experiment. Data for this animal, however, has been included in all cumulative data up to and including
2812183, when all animals were 20 weeks of age. i
I
1.3.2 Field Methods i
Beginning on 26th October, 1982, when kids were 2 weeks of age, and continuing until animals were 64 weeks of age, monthly fibre samples and skin biopsies were taken from the right mid-side position, i.e. from a point immediately behind the last rib and about half-way down the body. For sheep, this has been found to be a good ü,\& t 'average position'for fleece characters between the finer shoulder wool and the coarser breech (57). Fibre sampling alone was continued, each month, for a further 2 months. Following the methods of Carter (61) and Clarke (70) and Carter and Clarke (271) (280), with minor vatiations, samples were obtained as follows. Animals were restrained in the lateral recumbent position. Fibre was totally removed from the area of skin to be sampled by clipping with surgical scissors, then shaving with a scalpel blade. Fibre samples so obtained were carefully stored in small plastic bags until required for fibre population determination, and estimation of mean diameter of down fibre. t I {;
r 90
Following administration of 0.5 ml local anaesthetic (xylocaine with adrenalin), skin sample area was defined using a 1 cm stainless steel biopsy trephine by holding it on the surface of the skin and, with firm but not excessive pressure, twisting once to the right then once to the left, thus cutting through the epidermis and dermis
(Fig. 1 .1). The skin specimen was then removed using forceps and a sterile surgical scalpel blade to separate the dermis from the subcutaneous fascia (Fig. 1.2). The wound (Fig. 1.3) was treated ¿a* with ltlonacrin to prevent infection and, without exception, healed quickly. Skin specimens were placed immediately in Zenker's fixative solution (281) (Appendix ll). The biopsy trephine and forceps were kept in a solution of 100% ethanol when not in use. Subsequent fibre samples were taken in March 1985 when animals were 2 years of age, to determine the change in fibre diameter with increasing age.
1 .3.3 Laboratory Procedures
1.3.3.1 Skin Histology
Skin specimens were processed and embedded in paraffin wax as outlined in Appendix ll. Specimens were embedded so that the epidermal surface was as flat as possible and uppermost in the
paraffin block for, as pointed out by Burns (275), it is desirable to I ir ,g7"lñrJ^!4'id,
I Fig" 1.1 Showing definition of the biopsy skin area using a 1cm trephine.
Fig. 1.2 Showing removal of skin biopsy
Fig. 1.3 Showing wound area after removal of skin biopsy. ¡
t.:t4þ ß: {íÍ- .' t't q,t, r) I
91
avoid obliquely cut sections in studies of follicle population. With a Zeiss rotary microtome each paraffin block was serially sectioned at 10pm, beginning at the epidermal surface and ending at the base of the dermis. Total block sect¡oning was performed in this manner so that sections at the appropriate depth could be selected for determination of S/P ratio. Burns (275) found that half-way down the sebaceous glands of the primary follicles was an appropriate depth in Romney and English Leicester lambs. Short (278) also drew attention to the importance of the depth of counting of immature follicles if large discrepancies were to be avoided.
Lyne (1 18), however, considered it virtually impossible to observe all derived secondary follicles at only one level in the skin of Merino sheep, because of their derivation by branching. lt was pointed out by Holst et al (36) that in feral goats it is important to section just below the epithelial surface, as secondary follicles of these goats often do not extend to the sebaceous gland level of the primary follicles. Sections were floated onto a water-bath at 37o C, and picked up on numbered glass microscope slides coated with Mayer's albumin (Appendix ll). From 5-B sections were mounted on each slide and dried overnight in a 45o C drying oven. Sections were stained using the "Sacpic" method, also outlined in Appendix ll (57). 92
1.3.3.2 Estimation of Secondary to Primary (S/P) follicle ratio
A Reichert "Visopan" projection microscope was used to examine histological sections for determination of S/P ratio, using a magnification of 200X, obtained with a 1610.32 objective. Measurements were made at just below the epithelial surface where the sebaceous glands of the primary follicles were evident. Follicle groups were easily distinguished, trio groups being quite distinct as shown in Figs. 1.4 and 1.5. Where dual or quadruple
groups existed it was sometimes more difficult to recognize boundaries between groups. Where this occurred a whole group was taken to be all those follicles within an area which could be clearly defined as being separate from all groups surrounding it. lt should be pointed out, however, that dual or quadruple (or larger) groups were quite rare, the majority of groups being of the trio form. The number of groups examined in individual specimens was variable due to the varying quality of the sections, but was never fewer than 19 groups and was usually 36, the latter giving at least 100 primaries and their associated secondaries, from which to determine S/P ratio. Only follicles which contained a definite fibre were included in the counts (269). S/P ratio measurements are shown in Table 1.1. Total numbers of primaries and secondaries counted, and the ratio of these for each
animal, are shown in Tables A1-46 in Appendix l. Fig. 1.4 Cross section of kid goat skin showing distinct follicle groups, mainly of the'trio'form of three primary follicles (P) and
several associated secondary follicles (S). {Sacpic stain (57)}.
I
I
Fig. 1.5 A'trio'group of follicles comprised of three primary (P)
l i and several associated secondary (S) fibres. {Sacpic stain (57)}. i
I I t,
T' I
I I
T
I a
)
I
¡.î"'Ç- ¡ -Ê-. { I Ç Table 1.L: S/P Ratios of kids from 2 weeks to 64 weeks of age
Twins Twins Twins
I I I Date Age dsr Ç82 dss Qs4 css Ç8e Mean SE Meand SEd MeanQ SEQ (rveeks) Mean
26.r0.82 2 4.35 6.00 3.96 5.73 4.9t 3.60 4.76 0.39 4.4r 0.39 5.1 1 0.76 23.r1.82 6 4.76 6.00 4.30 5.92 6.00 4.43 5.24 0.37 5.02 0.72 5.18 0.7s t5.12.82 9 5.83 6.03 4.80 5.72 6.09 4.86 5.50 0.24 5.57 0.56 5.54 0.35 24.01.83 15 6.s8 7.t6 5.59 5.78 6.58 5.37 6.18 0.29 6.25 0.47 6.10 0.54 28.02.83 20 6.84 7.56 5.83 6.57 6.68 5.48 6.66 0.27 6.4s 0.44 6.54 0.60 30.03.83 24 7.74 7.03 6.52 6.83 5.86 6.80 0.31 6.93 0.10 6.7 t 0.55 29.04.83 28 7.40 6.84 6.40 6.93 5.85 6.68 0.26 6.89 0.0s 6.s5 0.4s 3.06.83 33 7.26 6.52 6.68 6.48 6.11 6.6t 0.19 6.50 0.02 6.68 0.33 1.07.83 37 7.68 6.83 6.62 6.79 5.77 6.74 0.30 6.81 0.02 6.69 0.9r 4.08.83 42 7.23 6.53 6.40 6.54 5.73 6.49 0.24 6.s4 0.01 6.27 0.42 30.08.83 46 7.08 6.52 6.02 6.50 5.70 6.36 0.24 6.51 0.01 6.27 0.42 29.09.83 50 6.98 6.07 6.09 6.73 5.77 6.33 0.23 6.40 0.33 6.54 0.45 31.10.83 55 7.00 6.44 6.64 6.29 5.89 6.4s 0.17 6.37 0.08 6.27 0.38 30.I 1.83 59 7.41 6.74 6.07 6.33 5.33 6.38 0.3s 6.54 0.2r 6.27 0.61 4.01.84 64 7.t8 6.6s 6.73 6.86 5.60 6.60 0.27 6"76 0.r1 6.50 0.47 ,I 93
.¡ ¿
ilI I t
I 1 .3.3.3 Statistical Procedures
.
Data was analyzed using the two-sample t-test to determine whether or not the two population means (male vs.female) for S/P ratio were equal at the 5% level of significance, and the relevant statistical data is shown in Table 1.2.
1.3.3.4 Fibre Measurement
For measurement of fibre population and estimation of mean diameter of down fibre, each fibre bundle was first trimmed slightly along the bottom (proximal) edge, to obtain an even edge, and then a single cut was made along this same edge, producing fibre snippets ol 1-2 mm in length which were allowed to drop onto a glass microscope slide into 3-4 drops of liquid paratfin. Using a blunt dissecting probe, fibres were evenly mixed and distributed in the paraffin and a coverslip was dropped on top. " The refractive index of animal fibres is 1.548, and mounting media having refractive indices near to this figure (see Table 1.3) (282), cause the detailed fibre structure, including scale margins, to appear indistinct or even disappear from view," and are therefore "excellent for fibre measurement where the image of the fibre in profile should have fine sharp edges without the complication of too much detail within the fibre being shown up (282)". Although liquid I I
I
-ì
Taete l-2
Data File: S/P Male Vs. Female kids Paired Samples... Variabl : Male Female Mean: 6.263 6.243 Std. Deviation: 0.716 0.493 Paired Observations: 1 5
t-stat ist ic: 0.270 Hypothesis: Degrees of Freedom: 14 Ho: p1 = þ2 Sig nif icance: 0.791 Ha: p1 * p2 Table 1.3: Refractive indices of some mounting media
Vy'ater 1.33 Glycerine 1.473 Cedarwood oil 1.5 13 Glycerine jelly 1.370 Gurr's M.A.C r.490 Polystyrene, in xylene 1.516 n-Heptane 1.385 Methyl methacrylate Gurr's Xam 1.521 Dioxan 1.412 Polymer r.495 Gu¡r's neutral mounting Triacetin r.431 Monomer: medium 1.527 Chloral hydrate 1.440 Unploymerized 1.417 Canada balsam 1.528 Lactophenol 1.444 Partially polymerized 1.427 Permount near to r.528 Chloroform 1.447 Toluene t.496 Methyl salicilate 1.538 Isobutyl methacrylate 1.450 Xylene r.497 Keratin of animal fibres 1.548 Carbon tetachloride 1.461 Euparal 1.500 Aroclor 1242 (Monsanto) 1.630 Polyvinyl acetate 1.467 Benzene 1.501 Gurr's Clearax 1"666 1.470 607o n lene 1.512
'Wildman, [From: A.B. (1954). 282] 94
paraffin has a refractive index of 1.470, which is somewhat lower than that of keratin, "it is still not low enough to cause undesirable optical effects (282)"; plus, it is inexpensive and readily available. A Reichert "Visopan" projection microscope at a magnification of 500X was used to measure the cross-sectionaf diameters of 300 (total coat) fibres. At this magnification, obtainable with the 40/0.65 objective, each division of the 200 mm measuring device is equal to 2pm or 0.002 mm. Fibres were individually measured; the measurement and cumulative count being recorded on data sheets. Two examples of data record sheets are shown in AppeÎO¡" l. Mean diameter of cashmere fibre was calculated as the mean of all non-medullated fibres measuring 30p or less per sample. Percentage of cashmere.fibre i.e. the number of non-medullated fibres measuring 30p or less, as a percentage of total fibre number, was calculated for each sample. Percentage and mean diameter were both recorded on the data sheet. The measurements for mean percentage and mean diameter of cashmere fibre are presented in Tables 1.4 & 1.5 respectively. Table 1.4: Mean percentage of cashmere fibre throughout the year. (*indicates samples from which it was not possible to estimafe percenlage of cashmere fibre due to a continuous fibre population from secondaries to primaries).
Twins Twins Twins I
I I I I I I Daæ Age dsr Ç82 dss Qs+ cf ss Ç8e Mean SE
26.t0.82 2 17.00 19.30 27.00 32.00 22.00 34.00 25.21 6.3 23.r1.82 6 17.00 59.00 29.33 42.33 27.70 23.66 39.s9 12.s6 Ls.12.82 9 19.30 70.60 51.00 33.67 22.67 14.00 39.51 16.52 24. 1.83 15 60.67 76.33 86.00 77.33 55.00 48.33 67.27 13.46 28. 2.83 20 8s.33 90.67 79.00 85.33 86.67 80.33 84.55 3.91 30. 3.83 24 87.67 8s.33 8s.00 86.33 81.00 85.06 2.24 29. 4.83 28 91.00 89.67 85.33 81.00 79.00 85.20 4.68 3. 6.83 33 87.00 86.33 89.33 81.33 79.67 84.73 3.63 r. 7.83 37 89.33 85.00 81.00 84.00 84"67 84.80 2.67 1 1'.) 4. 8.83 42 83.33 86.33 88.33 8s.33 82.00 85.06 30. 8.83 46 84.00 70.67 86.67 47.00 79.33 73.53 t4.34 29. 9.83 50 57.00 60.67 82.33 47.67 78.67 6s.27 13.19 31.10.83 55 5.33 20.67 7.33 5.67 21.00 12.00 '7.25
30. 1 1.83 59 6s.67 6.67 6.00 6.67 14.00 r9.80 23.t2 4. 1.84 64 59.00 7.33 64.67 12.00 7.67 30.13 26.00 ls. 2.84 70 75.00 80.00 85.00 82.33 75.00 79.47 3.97 13. 3.84 74 81.00 86.00 92.00 83.00 84.00 85.20 3.76 Table 1.5 Cashmere fibre mean diameter (pm). (*Indicates insufficient cashmere flrbre from which to calculate a valid mean) Twins Twins Twins
I I I I ^^ Daæ Age Cst Ç82 u85 884 Css Ç8e Mean SE
26.r0.82 2 * {< {< * *c {< {< 23.rr.82 6 * 11.86 1 1.81 9.39 14.76 * 1r.96 2.20 15.12.82 9 * t2.28 12.42 t2.70 14.38 {< 12.95 0.97 24.0r.83 15 12.ll t4.07 t2.69 13.87 15.r7 12.80 13.45 r.t2 28.02.83 20 14.53 15.34 t4.t7 13.76 t4.02 t3.67 14.25 0.62 30.03.83 24 15.35 14.44 14.08 14.57 t3.79 t4.45 0.59 29.04.83 28 14.65 t3.99 t3.4r 15.44 t4.26 14.35 0.75 3.06.83 33 t6.t9 13.75 14.33 15.30 14.25 t4.76 0.97 1.07.83 37 15.86 14.34 16.60 15.01 t4.62 15.29 0.93 4.08.83 42 15.34 13.54 16.t4 t4.9t 13.95 14.78 1.05 30.08.83 46 t4.37 14.72 15.98 13.66 14.44 14.63 0.85 29.09.83 50 t5.41 15.63 15.52 13.31 t4.07 t4.79 1.04 31.10.83 55 {< 15.78 * * 14.9t 15,35 0.62 30. r 1.83 59 13.55 :F * * 14.53 14.04 0.69 4.01.84 & 13.76 {< 13.55 13.38 *< 13.56 0.19 15.02.84 70 t4.30 13.01 14.50 13.06 t3.54 13.68 0.69 13.03.84 74 t5.t4 t3.46 t6.r2 t2.t4 r4.t4 t4.20 1.53 i It 95 t r :! I
t 1.4 RESULTS ¡ t
1.4.1 Skin lndividual changes in S/P ratio are shown in Figs. 1.6-1.8, twins being graphed together for comparison. Mean change in S/P ratio with age for all animals, included in Table 1.1 and shown in Fig. 1.9, shows a similar curve to that described by Schinckel (269) for follicle development in Merino sheep.
It can be seen that mean S/P ratio increased trom 4.76 at 2 weeks to 6.66 by the age of 20 weeks, but did not increase significantly beyond that age. There was, however, a decrease in mean S/P ratio at about 40 weeks of age (early August, 1983).
There was no difference at the 5% level of significance between
mean S/P ratio of males and females (Table 1 .2: Fig, 1 .10).
1.4.2 Fibre Characteristics
Fibre diameter distributions for each animal are shown in Figs. A1-490 in Appendix l. lndividual changes in percentage of cashmere
fibre are shown in Figs. 1 .11-1.13, and individual changes in mean diameter of cashmere fibre are given in Figs. 1.14-1.16. From measurement of mean percentage of cashmere fibre for all animals
as shown in Table 1.3 and in Fig.1 .17, il can be seen that by six weeks of age kids had an average of approximately 40/o of cashmere Fig. 1.6 Ghange in S/P ratio for kids No- 81 and 82 with increasing age. I 8
7
o (E 0É 6 o- t|, -#l- 5 81 -# 82 I
t\ 4 0 20 40 60 80
Age (Weeks)
Fig 1.7 Change in S/P ratio for kid No. 84 and 85 with increasing age. I
7
o 6 (ú E
CL U' 5
.+t- 85 4 + 84
3 0 20 40 60 80
Age (Weeks)
I
I Fig. 1.8 Change in S/P ratio for kids No.88 and 89 with increasing age. I
7
I o ct 6 cÉ
CL U' 5
-.+t- 88 4 '# 89
3 0 20 40 60 80
Age (Weeks)
I
i I i
I I t,
I
ll
I ,tr1
Fig. 1.9 Change in mean S/P ratio with increasing age of kids.
7.0
!
o 1, 6.0 GI cÉ
CL CN s.0
I
4.0 0 20 40 60 80
AgeMeeks
,i4
I
I
T
l Fig. 1.10. Comparison of S/P Ratio between male and female kids.
7.5
7.0
6.5 o (E 6.0 É.
CL 5.5 CI'
5.0
I Male S/P 4.5 Female S/P
4.0 0 20 40 60 80 Age (weeks)
l
I i t,
T I
I
ì
l Fig. 1.11. Change in mean T" ol cashmere with increasing age, kids 81 and 82. 100
80 o -o 60 o o E at, 40 ()ñl \o o\ #t- 81% 20 + 82%
0 0 20 40 60 80
Age (weeks)
Fig. 1 .12. Change in mean 7" cashmere fibre with increasing age, kids 84 and 85. r00
80 o ¡r o 60 o E E to (! o 40 ñ 85 "/o 20 -r¡---- 84"/o
0 0 20 40 60 80 i Age (weeks) Fig. 1.13. Change in mean 7o cashmere fibre with increasing agê, kids 88 and 89. f00
80 o ,ct o 60 o E an (õ 40 o \o o\ ...... +t- 88"/o 20 '..-----r- 89"/"
0 0 20 40 60 80
Age (weeks) Fig. 1.14. Change in mean cashmere fibre diameter with increasing age, kids 81 and 82. 17
16 t 15 o o ts 14 .g !, tr 13 (E o 81 = 12 82
11 0 '20 40 60 80
Age (weeks)
Fig. 1.15. Change in mean cashmere fibre diameter with increasing âgê, kids 84 and 85. 18
16 ¿J
o 14 o E .g tt 12 tr G o .+t- 85 10 = 84 I G 20 40 60 80
Age (weeks) Fig. 1.16. Ghange in mean cashmere fibre diameter with increasing âge, kids 88 and 89. 16 88 89 ¿ 15
C) o E 14 .g !t c (õ o r3 =
12 0 20 40 60 80 Age (weeks) Fig. 1.17. Change in mean o/o of Cashmere fibre.
100
o 80 -ct o o 60 E tt, o(5 40 s c (ú o 20 =
0 0 20 40 60 80
Age (weeks) 96
fibres in their coat. This percentage gradually increased to about 82/o at 16-20 weeks of age, and was maintained at approximately this level until 40 weeks of age, when the animals began to shed this coat.
lf data for mean S/P ratio and mean 7o cashmere fibre are compared
(Fig. 1 .18), it can be seen that both measurements reached a peak at the same point in time. Whereas mean percentage of cashmere fibre decreased again at between 40 and 45 weeks of age (i.e. in winter), once the secondary follicles were maturely established they then continued to produce fibres for the life of the animal. The slight drop in S/P ratio between 40 and 60 weeks of age coincides with the
winter shedding period (Fig. 1 .18), and as will be seen from subsequent work on seasonal variation in follicle activity in the adult animal, (Chapter 3) it is the usual time of shedding for animals in this environment. Also, the percentage of cashmere fibre, determined from skin biopsies, was compared to the percentage determined from fibre measurement (Table 1.6; Fig. 1.19). lt can be seen that there is very little difference in these measurements between 20 weeks of age,
by which time kids have attained their full complement of secondary follicles, and about 42 weeks of age, when they begin to shed. From the change in mean diameter of cashmere fibre for all animals
with increasing age (Table 1.5 and Fig. 1.20), it can be seen that mean diameter increased from approximatelyl2.00pm at 6 weeks of age to approximately 13.50pm at 64 weeks of age, 13 months later; Mean % Cashmere f!
J I NàCD@9 c, aSoocto o P o o j T' Ð 6', ¡u o c) o Þ a (o ! o Ð A' o{ È o o õ' (t,F 50) o. s o Ê, ct) o v, 3 o- l+ o
Àtotv=Date Age Mean Vo Mean Vo (Skin) (Fibre) 26.r0.82 2 82.22 20.88 23.tt.82 6 83.32 33.17 t5.72.82 9 84.64 35.20 24.0r"83 15 85.96 60.94 28.02.83 20 86.85 84.55 30.03.83 24 87.09 85.06 29.04.83 28 86.71 85.20 3.06.83 33 86.83 84.73 1.07.83 37 87.00 84.80 4.08.84 42 86.59 8s.06 30.08.83 46 86.36 73.53 29.09.83 50 86.57 65.26 31.10.83 55 86.33 12.00 30.1 1.83 s9 86.24 19.80 4.01.84 64 86.88 3s.83 Fig. 1.19. Gomparison olo/o Cashmere from S/P Ratio and from fibre analyses. 100 88
87 80 o 86 tr ¡l .Y at, 85 60 o o o 84 o E E t (t, 40 tt, (! 83 (! C) o 82 ñ 20 s 81
0 80 0 20 40 60 80 * o/o (flbre) Age (weeks) * %(Skln) Fig. 1.20. Change in mean diameter of cashmere fibre from 6 weeks lo 74 weeks of age.
16
E 15 l- o) o 14 E .gõ c 13 (E o
= 12
11 0 20 40 60 80 Age (weeks) 97
a
l an increase of 1.50pm. lt is also evident from Table1.5 and Fig.
j 1.20, that fibre diameter increases early in the growing season, to a i
I diameter of approximately 14.5-15.0¡rm which is maintained until ð .á rl been winter, when fibre diameter decreases once more. lt has ¡ shown, for sheep, that when fibres begin to grow the tip is seen as a Ì l narrow point which gradually broadens as fibre growth progresses I (64) (56) (283). This probably explains the early increase in fibre diameter. lf fibre diameter measurements for the months of November through March are compared for 1983 and 1984, it can be seen that fibre diameter did not increase much in the second season (when animals were just over one year of age). Subsequent fibre samp¡es, taken from remaining animals at two years of age, however, showed an increase in fibre diameter lo 16.77¡tm (Table 1.7; Fig. 1-21). Diameter had increased by about 2¡rm by 2 years of age.
1.5 DISCUSS¡ON
It seems, then, that in the Australian cashmere-bearing goat all secondary follicles have matured by the age of 20 weeks. These results are similar to those obtained by other workers in New South Wales (39), who found that development of the follicle population continued until four months of age in the feral goats which they studied. Month/Year 82 85 84 88 89 Mean
Mar-83 15.35 14.44 14.08 14.57 13.79 14.45 Mar-84 15.14 13.46 16.12 12.14 14.14 14.20 Mar-85 18.19 15.59 15.1 6 17.18 16.00 16.42
TABLE 1.7 CHANGE IN DüAMETER OF CASHMERE FROM 4 MONTHS TO 2 YEARS 4 MONTHS. Fig. 1.21. Change in mean diameter of cashmere in kids, from 5 months to 2 years 5 months. 20
19 Y = 12.433 + 1.1050x R^2 = 0.865 E F 18 o 17 o) (l) E I E 16 E ,g E tr 82 E 15 o 85 E 3 (ú E o 14 T E 84 = o o 88 13 I 89 12 March 1983 March 1984 March 1985 98
Lambert et al (39), however, found that male kids had higher S/P ratios than females at birth but were similar thereafter. This was not found to be the case in this experiment, as shown in Fig.1 .10; on the contrary, S/P ratio for females at 2 weeks of age was found to be higher than that for males, but the difference had disappeared by 6 weeks. However, due to the small number of animals sampled it is concluded that this initial difference was due to sample variation only. Dreyer and Marincowitz (254) found that Angora goat kids had an S/P ratio of about 2.00 at birth, but that by 3 months of age all secondary follicles had matured and the S/P ratio was 8-9. They also found that females reached the mature ratio earlier than castrated males, but that by 6 months of age this discrepancy had disappeared. These differences between male and female kids were not found in this experiment (P>0.05). Clarke (261) showed that the S/P ratio for feral goats in eastern Australia falls between that for the milk and Angora breeds. He found the follicle population to be approximately 20.0 per. sq. mm and the S/P ratio to by approximately 6.68 (range 5.85-7.74), taken from calculations at28 weeks of age. Thus, it seems that South Australian feral-based animals are similar, in regard to their S/P
ratio, to those in eastern Australia. A comparison of S/P ratio for several goat breeds and several sheep breeds, compiled from various sources, including those studied here, is shown in Table 1.8.
There are possibly two (associated) reasons for the decrease in Table 1.8: S/P ratios for various breeds of goats and sheep Goats
Br eed source S/P milk Clarke, L977 3.70 Saanen Ryder, 1966 3.00-5.00 Toggenburg Ryder, 1966 2.50-3.90 Red Sokoto Burns, 1965 4.00-5.00 Aust. ferals Clarke,1977 5.80-7.00 Aust. ferals Present study 6.60 Saanen x Toggenburg Ryder, 1966 6.00 Angora Clarke,1977 6.40-9.10 Angora Dreyer & 9.20 Marincowitz,196T
Sheep
Breed Source S/P
Indian 'hair' sheep Ryder, 1983 <2.00 'Wiltshire Horn Ryder, 1983 3.50 Soay Doney etaL,I974 3.80 Borderlæicester Carter, 1955 4.40 Cheviot Carter, 1955 4.50 Suffolk Carter, 1955 4.80 Dorset Horn Carter, 1955 5.40 Spanish Guirra Ryder, 1983 5.70 Southdown Carter, 1955 6.30 Swedish Landrace (f,rne) Carter, 1955 7.t0 Spanish Merino Ryder, 1983 10.00 Coriedale Carter, 1955 10.80 Polwarth Carter, 1955 12.80 Aust. Camden Park Merino Carter, 1955 14.00 (from McArthur's sheep) Austalian Merino (strong) Ryder, 1983 16.50 (fine) Ryder, 1983 19.10 (medium) Ryder, 1983 21.00 i:
i ¡ i :ã
a
99 mean S/P ratio between about 40 and 60 weeks of age (Fig. 1.9). Firstly, some secondary follicles would have become inactive at this stage and would have receded toward the epidermal surface of the skin, forming brush ends to fibres, and producing dormant dermal papilla, in readiness for shedding. Therefore, in histological sections, some of the follicles may have been at too shallow a depth to be included in S/P ratio estimates. Secondly, there is evidence from Figs . 1.17 and 1 .18 that some down fibres have already shed at I percentage of fibre in the total coat this time, as the down i t decreased from 85.0% in early August, 1o73.5/" in late August. ln I histological sections follicles which were not producing fibre would not have been included in the estimate of secondary follicles for S/P ratio determination. The slight drop in S/P ratio was in mid-winter, which is the usual
time at which shedding begins in the adult animal in this environment (Chapter 3). Similary, McDonald et al (284) have shown
that cashmere growth ceases in June-July in another population of Australian goats at a slightly different latitude. Restall et al (40), similarly found a decrease in secondary follicle density during the autumn and winter months in feral goats. They found that this was highly correlated to live weight, the density decreasing with an increase in weight, and suggested that the observation may have been an effect of skin expansion. S/P ratio, however, is not affected by either skin expansion or retraction, and therefore it is more likely.that changes in S/P ratio observed here were due to reasons proposed above. 100
ll From this it can be concluded then, that with two-coated animals it would be better to make estimates of S/P ratio at times other than when the animal is preparing to shed the old coat. That fibre diameter increases early in the growing season, reaches a maximum over summer, and narrows again in autumn/winter is consistent with observations from other animals. lt has been shown, for sheep, that when fibres begin to grow the tip is seen as a narrow point which gradually broadens as fibre growth progresses (56) (64) (283). The observation that fibre diameter decreases again in autumn is also in keeping with observations from sheep, which showed a narrowing of wool diameter in winter (112) (285). Although it has been shown that nutritional changes can alter fibre diameter in sheep (100), this seasonal variation in fibre diameter I I was found to be independent of any nutritional effect (193), and was f, I quite variable between breeds, being most evident in the British mountain breeds and in those which tend to shed their fleece (57)
(1 12) (285). lt was shown by Margolena (115) that in Ramboullet
rams, which do not shed, cell division of the follicle bulb nevertheless tended to slow down during the winter months to about
72o/" of that found in early summer. Rudall (286) suggested that changes in the dimensions of the papilla are the principal cause of
variation in fibre output, i:e. in winter, the height of the papilla was depressed, being about two{hirds of the summmer height, although metabolic efficiency could alter too.
Narrowing of the fíbre in winter, then, is probably due to a decrease in follicle activity in preparation for shedding of fibres. An investigation of these aspects of fibre production has been made and
is detailed in Chapter 3.
It can be seen (Fig. 1.19) that there is very little difference between
percentage of cashmere fibre determined from total fibre
population, or that determined from skin biopsies (S/P ratios) , I between 20 weeks of age, by which time kids have attained their i i t age, J full complement of secondary follicles, and about 42 weeks of ¡ I I when they begin to shed. t I
That percentage of cashmere fibre determined from fibre { i measurement is always slightly lower than that determined from
I due to I follicle ratios in the skin, can be explained by the fact that 1 the often large differences in size between cashmere fibres and d guard hair fibres, it is likely to be more common to overlook iê ,.1 cashmere fibres during measuring. Because of their large size, it would be less likely for guard hairs to be overlooked. Thus, although S/P ratio can be used to select animals from as early as 20 weeks of age, it can be seen that percentage of down fibre in the coat of the animal, whilst not as precise, is a good estimate of secondary follicle development and proportion. Estimations from fibre samples are quicker, easier, cheaper and more practical to perform than S/P ratios from histological sections, and are less stressful for the animal. Therefore, it is suggested that, at least for kids born in October, fibre sampling be used to select between l animals for production purposes, and that this should be done I between the ages of 20 and 40 weeks. ;
r 102
The animals in this present experiment were born in October (spring), at the beginning of the cashmere growing season, and the pattern of down fibre development and shedding was identical to that for adult animals (see Chapter 3).
It will be interesting to determine whether or not animals born at other times of the year, e.g. autumn, follow in their first year the adult pattern of down fibre growth and shedding as did these animals born in October.
ri i{t .i
I
T @haptcv 2
A Gomnparüson of Sceondany Fo[[üe[c Deve[opmncnt [n Goat Ktds tsonn at
Eüffcnent Tümncs of thc Yeatr"
I
T
I 103
2.1 ABSTRACT
Cashmere fibre development was compared in two groups of kid goats, born at different times of the year, in order to determine any differences in the pattern of development due to seasonal influence.
The first group of kids were the three sets of twins studied in
Chapter 1 , which were born in October (spring), 1982. The second group was comprised of two sets of twins (one set a pair of males,
the other a male and a female), one female kid from a set of twins whose sibling had died at birth and a single female kid. These
animals were born in April/May (autumn), 1989. Thus, each group of animals was comprised of 3 males and 3 females.
I Changes in both percentage and mean diameter of cashmere fibre with increasing age were compared between the two groups of kids.
It was found that the second group, (born in autumn), showed a much more rapid development of cashmere fibre than did the first group, (born in spring). Autumn-born animals showed a full complement of cashmere fibre in the coat by about 7 weeks of age, whereas the spring-born animals did not show full development of their cashmere coat until 16-20 weeks after birth. These differing rates of secondary follicle development coincide with varying rates of follicle activity between autumn and winter in the adult animal, maximum activity being observed in autumn and minimum
I activity in spring (chapter 3). lr ,ti ií 104 '! i I :
It is suggested that season/daylength is a major factor in determining the rate of development of secondary follicles in cashmere goats.
2.2 INTRODUCTION
Goats are usually seasonal breeding animals which have a definite rutting season lasting about 5 months. The breeding season coincides with shorter days (long nights), and in Australia begins about March and lasts until about July, but probably varies depending upon the environment, (latitude) (287). Kids are born five months later, usually in spring. However, some goats kid as early as April/May and some producers prefer to have their animals kidding in July.
It was shown in Chapter 1 that kids born in spring (October) had reached their full complement of cashmere fibres by about twenty weeks after birth and that cashmere percentage, determined from fibre samples, was a good approximation of the proportion of fully developed secondary follicles at that time.
However, the animals sudied in Chapter 1 were born, and began developing and producing their secondary fibres at a time when, in the adult animals, the new season's cashmere fibre is just starting to regrow, and thus, showed a pattern of fibre development and growth identical to that of adult animals (Chapter 3). The follicles developed slowly over a period of about 20 weeks by which time 105
secondary follicles were responsible for producing approximately 82/" of the total coat. This proportion was maintained until the following winter/spring when the percentage of cashmere fibre in the coat fell significantly to about 12/", at the time at which shedding usually occurs in the adult animal. As growth of cashmere fibre is influenced by season, and in particular daylength, at least in the adult animal - i.e. actively growing during spring and summer, slowing down in autumn and ceasing growth in mid-winter (Chapter 3) - it is possible that the pattern of cashmere fibre development in the coat of kids born at different times of the yeat, may be different. This hypothesis, however, would assume that the influence (presumably hormonal), activated by changes in daylength, could have variable etfects upon any autonomous developmental pattern of the follicles themselves. The purpose of the present experiment, then, was to determine whether or not there are differences in the pattern of cashmere fibre development in kids born at ditferent times of the year, i.e. spring and autumn, in order to gain some evidence as to whether or not season plays any part in secondary follicle development. 106
I :
2.3 MATERIALS and METHODS
The experimental animals were two groups, each of six kids, each group comprised of 3 males and 3 females. The first group of kids (Group 1) were the three sets of twin kids used in the study of cashmere fibre development in Chapter 1, born in October (spring), 1982. The second group of goats (Group 2) consisted of two sets of twins (one set a pair of males, the other a male and a female), one female kid from a set of twins whose sibling had died at birth and a single female kid. This second group of animals was born in April/May (autumn), 1989. Animals of the first group were weaned at 3 month of age and were then pastured at the Waite Agricultural Research Institute and subject only to usual farm practices, with supplementary feeding when necessary. The second group remained with their mothers throughout the sampling period of 6 months, was housed indoors in pens but subject to normal external daily lighting, and fed the usual shed ration of lucerne chaff and goat pellets. (The mothers of these kids were used in a study of the effect of pregnancy and lactation upon secondary follicle activity which will be discussed in
Chapter 5). Fibre samples were taken from Group 1 at monthly intervals (Chapter 1), and from the Group 2 at fortnightly intervals. Percentage and diameter of cashmere fibre for Group 2 animals were calculated as for Group 1 in Chapter 1 (1.3.3.4). 107
2.3.2 Statistical Analysis
The mean data for the two groups was analyzed using the two-sample t-test to determine whether or not the two population means were equal at similar ages, with regard to percentage of cashmere fibre in the coat.
I l;1
2.4 RESULTS lndividual and mean measurements of percentage and diameter of cashmere fibre for Group 2 animals are shown in Tables 2.1 and
2.2, respectively, and these results are presented graphically in Figs. 2.1-2.8. The data for Group 1 animals is presented in Tables 1.3 and 1.4 in Chapter 1 and is therefore not repeated here. ln order to compare the autumn-born animals (Group 2) with those born in spring (Group 1), the change in mean percentage and mean diameter for the two groups is depicted graphically in Figs. 2.9 and
2.10. The animals in Group 2 were studied only up to the age of 29 weeks, and therefore only the data to approximately the same age (28 weeks) for Group 1'animals have been used as a comparison. It can been seen, immediately, that there is a significant difference in the rates of secondary follicle maturity, (gauged from increasing percentage of cashmere fibre in the coat), between the two groups of kids. Whereas Group 1 animals did not reach a full complement of cashmere fibre until about 16-20 weeks after Table 2.L: lVlean percentage of Cashmere fibre from Group 2 kids born in autumn
Twins Twins
I I I Date Age Õ tgt Ç1e8 Crso Çles Õß+ Ç 183 Mean SE MeanQ SEQ Meand SEC (weeks)
16.05.89 J 7.00 14.00 20.50 4r.50 52.00 8.00 23.83 7.63 23.00 10.00 24.67 13.80 30.05.89 5 25.00 65.50 71.00 71.00 77.00 58.00 6r.25 7.70 55.67 15.30 66.83 5.53 13.06.89 7 70.00 78.00 81.00 87.00 75.50 77.50 78.17 2.3r 79.33 4.98 77.00 0.76 27.06.89 9 79.50 83.00 83.50 81.50 75.00 80.00 80.42 1.26 81.50 1.15 79.33 2"33 11.07.89 1t 79.50 74.50 85.50 85.50 67.50 82.00 79.08 2.86 83.50 2.00 74.67 4.t9 25.07.89 13 79.00 77.50 81.00 84.50 73.s0 88.00 90.s8 2.t0 8r.50 1.61 79.67 4.32 8.08.89 15 78.50 79.50 80.00 89.00 78.50 81.50 81. 17 1.63 82.50 3.28 79.83 0.88 22.08.89 t7 79.00 78.50 84.50 86.50 83.00 84.00 83.08 3.33 83.33 2.24 81.83 1.09 5.09.89 19 6s.00 78.00 75.50 78.00 75.00 74.50 74.33 1.96 72.83 3.98 7s.83 1.09 19.09.89 2t 68.00 76.00 75.4r 79.00 68.00 77.00 73.99 1.93 74.14 3.24 73.67 2.85 3.10.89 23 72.00 74.00 73.00 79.00 76.s0 71.50 74.33 1.18 74.67 2.r9 74.00 r.44 17.10.89 25 6s.00 65.50 31.50 8s.00 50.50 72.00 61.5 8 7.55 60.50 15.60 62.67 6.37 31.10.89 27 67.s0 78.00 64.50 85.50 70.50 73.50 73.25 3.11 72.s0 6.s6 74.00 2.18 15.11.89 29 70.50 77.50 52.50 83.50 59.00 81.00 70.67 5.1r 68.83 8.99 72.s0 6.83 Table 2.2: Mean diameter of Cashmere fibre from Group 2 kids born in autumn
Twins Twins
I I I Daæ Age Õ tgt Ç1e8 drso Q1e5 Õ ts+ Qts: Mean SE MeanÇ SEÇ Meand SEC (weeks)
16.05.89 3 10.86 lt.2t t2.44 11.66 12.35 11.38 11.65 0.58 11.65 0.65 11.65 0.s0 30.05.89 5 12.48 11.60 t4.27 12.42 13.81 12.69 12.88 0.90 13.06 0.86 12.70 0.90 13.06.89 7 13.00 12.00 13.96 12.00 14.54 13.54 13"r7 0.95 r2.99 0.80 13.36 1.05 27.06.89 9 1,3.32 r2.76 14.38 11.90 r3.84 13.77 13.33 0.81 13.20 1.02 13.46 0.49 11.07.89 11 13.82 t5.02 r4.87 tr.97 15.01 15.22 14.32 t.t4 r3.55 r.20 1s.08 0.10 2s.07.89 13 r5.00 15.10 ts.46 12.27 15.50 15.34 14.78 t.t4 14.24 r.4t 15.31 0.16 8.08.89 15 15.63 15.69 13.94 12,81 14.87 16.43 t4.90 t.2t 14.t3 1.16 15.66 0.64 22.08.89 l7 14.75 15.65 13.85 13.77 14.88 14.53 14.73 0.78 14.46 0.92 15.02 0.47 5.09.89 19 r5.82 15.76 r3.48 13.60 14.12 15.03 t4.64 0.96 r4.30 1.08 14.97 0.67 19.09.89 2T 15.35 15.10 r3.91 13.27 13.90 14.22 14.29 0.72 14.18 0.87 T4.47 0.51 3.10.89 23 14.83 14.62 t3.62 13.23 13.7t 13.42 13.91 1.60 13.89 0.68 t3.92 0.51 17. r0.89 25 13.95 14.22 t4.40 t2.73 13.22 13.74 13.7t 0.58 13.69 0.7 | 13.73 0.41 31. r0.89 27 14.47 14.49 13.95 12.86 13.68 t4.r9 13.94 0.56 t3.76 0.67 t4.t2 0.33 15.11.89 29 14.79 14.81 t4.97 12.49 14.27 14.08 14.24 0.84 14.08 1.13 14.39 0.31 Fig. 2.1. Change in mean o/o of cashmere with increasing age of Autumn-born kids 197 and 198. 100
80 o ¡t o 60 6) E (t, 40 oo 197 s -t+l- 20 + 198
0 3 5 7 911131517192123252729 Age (weeks)
Fig.2.2. Change in mean o/o of cashmere fibre with increasing age of Autumn-born kids 186, 195. 100
o 80 .ct
o) 60 o Ë Ø oct 40 -oo\ 186 20 * 195
0 c)tol\o)Fcl r¡t otFetútl\O) F Fô¡ô{NNôI Age (weeks) Fig. 2.3. Change in mean !" ol cashmere fibre with increasing age of Autumn-born kids 183,184 (twins). 100
(¡) 80
..c¡
o 60 o E (!ut 40 C)
* --l- 184 20 --* 183
0 etgtl:ol(tlo
