Avian Genetic Diversity: Domesticated Species

Avian genetic diversity: Domesticated species

GENETIC DIVERSITY IS CONSIDERED crucial to the bird stocks (ring-necked pheasant and bobwhite continued survival of a species, be it wild or do- quail) have been developed and will be noted in mestic. Such within-species diversity has been this report. Noted below are salient features of the raw material of agriculturists over millennia. the most widely used domesticated species that In response to selective breeding and the differ- have the greatest need for conservation of ge- ential survival of less fit animals, preferred traits netic stocks. have been accentuated and clustered to produce distinct breeds and varieties of the modern do- Chicken mesticated species (NRC 1993). In more recent times, researchers have deliberately isolated First domesticated over 6,000 years ago, the various mutations in specialized stocks, permit- chicken (Gallus gallus or G. domesticus) presents ting the systematic study of such mutations and by far the greatest amount of genetic diversity of promoting a better understanding of the normal the domesticated avian species, with over 400 function of the affected genes. identified genetic variations (SOMES 1988). Many The totality of wild and domesticated species are showcased in the more-than 100 recognized form the gene pool or genetic resources base chicken breeds and commercial varieties, which necessary for the survival of the species. The variously integrate most of the naturally occur- genes and genotypes present in this pool repre- ring mutations affecting size, body type, produc- sent genetic resources which are accessible and tion characteristics, posture, color, feather can be exploited by biologists and breeders. In structure and location, comb shape, and behav- this report, we emphasize “genetic stocks” which ior (see Figures 1 and 2 for wild- and domestic- have been bred for specific traits and genes in type chickens). Some of the most extreme vari- contrast to breeds in which the individual birds ants include: the tiny, short-legged Japanese have many traits in common and can generally Bantam; the tall, aggressive Old English Game be maintained with randomly breeding populations. Genetic stocks are typically selected for traits of special interest to breeders and geneti- cists. Many of them are reproductively, physi- cally, or physiologically compromised, and re- quire special care in breeding and management, even for maintenance or conservation purposes. Target species While the AGRTF recognizes the need for conservation of undomesticated avian species, this report primarily addresses the need for conservation of specialty stocks of domesticated species, particularly chicken, turkey, and Japanese quail. A limited number of waterfowl (duck and Figure 1. Red Jungle Fowl rooster from UCD 001 goose) genetic stocks and semi-domestic game- (Photo courtesy of J. Clark, University of California–Davis).

5 Fowl; the light-weight Single- Box 5. Parthenogenetic turkeys comb White Leghorn hen that can lay more than 300 eggs in PERHAPS THE MOST SPECTACULAR use of tur- hatch, and grow into fully functional her first year of production; and keys in experimental biology was the males (OLSEN 1965). The existence of the large Rock-Cornish commer- study of meiosis, fertilization, and early this line has given rise to the notion embryonic development with a strain that genetic imprinting does not exist cial meat chicken, with its phe- of parthenogenetic turkeys. In the in birds, although this conclusion must nomenal rate of growth and 1960s and 1970s, M.W. Olsen of the be tentative in the absence of any for- well-fleshed carcass. These are United States Department of Agricul- mal investigation of imprinting in the all thought to share a common ture Agricultural Research Center at unique parthenogenetic stock. How- ancestor in the Red Jungle Fowl Beltsville developed a line of turkeys ever, this parthenogenetic stock exists in which an embryo would form in 30 precariously at only two research sta- (G. gallus gallus) (Figure 1) to 50% of the unfertilized eggs (par- tions in the world (the University of which is still found wild in parts thenogenesis). Most of these embryos Guelph (Ontario, Canada) and the Uni- of India and Southeast Asia die, but a small proportion of them versity of Oman). (CRAWFORD 1990; FUMIHITO et al. (about 0.5%) continue to develop, 1994), although some poultry specialists believe that several other jungle fowl species (G. sonnerati, G. lafay- ettei, and G. varius) also contributed to the an- cestral gene pool (CRAWFORD 1990).

Turkey The one commercially important avian species originating in North America, the domestic turkey of commerce, is the product of hybridization between two subspecies of turkey: the domesticated Meleagris gallopavo gallopavo from Central America and the wild M. g. sylvestris from the eastern United States (CRAWFORD 1990). From these hybrids, birds were selected for size, tame- ness, carcass yield, and rapid growth, resulting in several distinct breeds and varieties (Figure 3). The modern commercial or exhibition turkeys are large, slow-maturing birds with a much lower reproductive potential than chicken or Figure 3. Flock with different turkey breeds (Photo Japanese quail (at one generation per year for courtesy of F.A. Bradley, University of California–Davis). the turkey). Although this species is far less popular with researchers or hobbyists than the chicken or the Japanese quail, at least six breeds are still kept for exhibition and a few unique research stocks have been developed (Box 5), including several commercial-type long- term selected and randombred-control lines kept at Ohio State University (see survey results, Ap- pendix 2, Tables 2.1 and 2.2). Perhaps as a con- sequence of the few researchers studying the turkey, relatively few mutations (49) have been reported in the turkey compared to the chicken and Japanese quail (SOMES 1988).

Japanese quail

Gaining in popularity as an experimental animal in both research and education, the Japanese quail (Coturnix japonica) is a small, early matur- Figure 2. White Leghorn rooster from UCD 003 (Photo ing, highly efficient egg and meat producer. Until courtesy of J. Clark, University of California–Davis). recently, the Japanese quail was classified as a

6 subspecies of the common European quail (C. productive life of an individual bird is quite coturnix). It is now classified as a distinct species short, frequently less than one year, and, unlike because of the nonhybridization of the two in the the chicken, close inbreeding is not tolerated. wild or in captivity (CHENG and KIMURA 1990). Thus, only one moderately inbred line exists (at According to all available documentation, the the University of British Columbia). domestic Japanese quail strains used in meat and egg production (even in Europe) are descen- Duck ded from C. japonica, which is still found in small wild populations in Japan. While gaining Almost all of the 15 or so domestic duck breeds popularity as a food animal in the US, its small recognized today are descended from the wild size has limited its use as a meat- or egg-pro- mallard duck (Anas platyrynchus platyrynchus), ducing animal to specialty markets. However, the exception being the Muscovy duck (Cairina the Japanese quail has other qualities that make moschata) (LANCASTER 1990). In addition to the it ideally suited for research. Usually reaching different plumage patterns and colors, a variety sexual maturity by six weeks of age, the females of body types and behavioral traits are found often lay an egg a day for several months. The among the duck breeds, ranging from the boat- males are aggressive breeders and maintain high shaped, vocal Call ducks to the cane-shaped In- fertility even when housed with four or more dian Runner ducks. Only 22 mutations have hens. The early maturity and short incubation been described in the domestic duck, most in- interval (16 to 17 days) permit as many as five volving feather color or pattern (LANCASTER generations in a single year, in contrast to the 1990). As such, these traits have been used in slower-maturing chicken (one to two generations defining breed and variety standards, especially per year) or the even slower maturing and less among the more ornamental duck breeds, such productive turkey (one generation per year). The as the Call, Indian Runner, Crested, Cayuga, quail is sometimes called the mouse of the bird and Swedish. While such breeds are usually world, since it has become extremely popular as only kept by hobbyists, a few are important in a model species for biological research in several commercial meat production, particularly White fields, including toxicology, cell biology, nutri- Pekins, Rouens, and, in some areas, Muscovy or tion, and selective animal breeding. Although Muscovy-domestic duck hybrids. most researchers use unselected or randombred birds, over 100 mutations are known in this spe- Goose cies, including many affecting feather color and shape (Figures 4 and 5), and several causing Six recognized domestic goose breeds were de- embryo-lethal deformities (SOMES 1988; CHENG rived from the western Greylag goose of Europe and KIMURA 1990). At present, most of these mu- (Anser anser anser). Several other breeds are tant strains are only maintained at the Univer- thought to have descended from the smaller sity of British Columbia or by hobbyists. Two Swan goose of central Asia (A. cygnoides). The drawbacks with this species are that the usual African breed is believed to be derived from a

Figure 4. Japanese quail silver mutation from UBC SI Figure 5. Japanese quail porcupine mutation from (Photo courtesy of K. Cheng, University of British Co- UBC PC-WB (Photo courtesy of K. Cheng, University lumbia). of British Columbia).

7 hybrid between these two species (HAWES 1990). and pheasant blood-type variants currently kept Strict herbivores, geese have a long history of at Northern Illinois University (JARVI et al. 1996). domestication, but their delayed maturity (two years) and low egg production rate make them Types of genetic stocks less attractive as an experimental animal or as a commercially viable species (Box 6). However, For the purposes of this report, genetic stocks due to the increasingly diverse consumer groups are classified into four categories that reflect the in the US and Canada, formerly noncommercial genetic composition and type and the breeding species are becoming popular on a small scale system used to maintain them. for specialty markets. One example is the demand from the Asian markets for a smaller, less • Randombred fatty meat goose. Until now, Europeans and • Highly inbred North Americans have traditionally raised Emb- den geese for market purposes. This large-bod- • Long-term selected ied, fatty bird is not well suited to the method of • Mutant (including cytogenetic variants cooking employed by Asian chefs. Therefore, wa- and transgenics) terfowl suppliers are now starting to grow the smaller Chinese geese for this market. We are primarily concerned in this report with conservation of genetic stocks developed for Gamebirds research purposes, which include all of these categories. Conservation of genetic stocks in the Several species of game birds are commonly different categories present different challenges bred commercially or by hobbyists, including for successful conservation, including: high em- many subspecies of the Ring-necked pheasant bryonic mortality, low viability, poor reproduc- (Phasianus colchicus) and the Bobwhite quail tive traits, pronounced susceptibility to one or (Colinus virginianus). Nine color mutations have more diseases, large and deleterious genetic been identified in the pheasant, along with sev- load, poor response to specific environmental eral affecting skin color and feather structure, stressors, poor recovery of cryopreserved semen, and 11 that produce biochemical polymorphisms and need for a very large gene pool (more than (SOMES 1990). For most populations, very little 100 birds per generation). selective breeding or inbreeding is deliberately practiced, and the development of gamebird Randombred lines are maintained as relatively stocks for genetic research is unusual. Excep- large populations of birds (usually over 100) in tions include the now-extinct inbred pheasant which little, if any, selection of breeding stock is lines developed at the University of California– done by the curator. Quite simply, the number Davis (WOODARD et al. 1983) and the Bobwhite of progeny from each male or female depends on the reproductive success of that bird at the time the eggs are col- Box 6. Research with goose breeds in Canada lected to reproduce the population. Such randombred stocks WHILE GEESE ARE NOT COMMONLY used for and improving egg production with experimental purposes, a relatively controlled lighting and trapnesting. are generally kept as closed large experimental population of geese Early studies with Pilgrim geese (the flocks, although new bloodlines was maintained at the Center for Food only goose breed that shows strong may be introduced to the popu- Animal Research (CFAR) in Ottawa. Sev- sexual dimorphism) included a demon- lation to improve the vigor of the eral distinct stocks of Chinese, Emb- stration of increased egg production flock, particularly if inbreeding den, and Chinese X Pilgrim hybrid with selection (MERRITT 1962), and use geese were developed in Ottawa to of light control to increase egg produc- depression is observed. The study production traits and DNA fin- tion. More recently, artificial insemina- birds may be reared and bred in gerprinting patterns (GRUNDER et al. tion techniques have been improved a single large enclosure, with all 1994). The stocks included standard (GRUNDER and PAWLUCZUK 1991) and males having access to all fe- breed control strains, stocks selected geese have been shown to lack endog- males. This is a common for for multiple traits, and the unselected enous viruses (i.e., viral DNA integrated pheasants, ducks, geese, some reference strains (SOMES 1988). As with into the host bird chromosomes) of the chicken and turkey research in the early avian leukosis type (GRUNDER et al. chickens, and naturally breed- part of this century, most studies with 1993). Unfortunately, with the loss of ing turkey stocks. Alternatively, the relatively undeveloped pure and funding from the Canadian govern- the birds may be randomly seg- crossed goose varieties have been re- ment in April of 1997, these stocks regated into smaller floor pens lated to agricultural objectives, includ- were either eliminated or dispersed. or randomly paired or grouped ing methods of rearing broiler geese in cages, as is common with

8 Japanese quail. A minimum of 25 pairs, usually Highly inbred genetic stocks are invaluable in more than 150 birds, is needed to keep inbreed- a wide range of research fields, particularly ing at a minimum. These stocks are often kept genomics (gene mapping) and immunogenetics as a source of “normal” control birds, and also (Box 7). A good example of the usefulness of in- function as a resource stock, from which inbred bred strains in genomics is the mapping of clas- or selected stocks can be derived or qualitative sical mutations. While over 80 classically identi- mutations isolated. fied genetic mutations have been assigned to the chicken linkage map, only a few have been lo- Inbred lines are produced by breeding together cated on the molecular map. This is due to the close relatives for many generations, resulting in lack of genetic characterization of the exhibition increasingly homozygous and homogeneous breeds and lines in which most of these muta- progenies. Different types of mating schemes are tions are found. Such nonuniform genetic back- used, depending on how rapidly the researcher grounds make them difficult to use in matings is attempting to approach complete homozygos- designed to integrate the maps. In contrast, ity. Disregarding parthenogenesis, the most congenic lines, mentioned above, are uniquely rapid inbreeding is produced by father-daughter, useful for such genetic mapping. The integration mother-son, or brother-sister (full-sib) matings. of genes in exhibition breeds into defined inbred These breeding schemes can also be used to ex- lines would provide the necessary uniformity for pose deleterious recessive traits or to fix pre- molecular mapping of these traits. ferred or beneficial single-gene traits in a population. Unfortunately, even in the absence of ma- Long-term selected stocks are the result of jor genetic defects, the fertility and viability of many generations of testing and selective breed- the inbred offspring are almost always lower ing for traits governed by multiple genes (the so- than the more outbred parent strain, a charac- called quantitative or polygenic traits). Many val- teristic called inbreeding depression. If selection ued heritable characteristics in the poultry and breeding strategies do not compensate for breeds belong in this category. These include egg this decline, inbreeding depression can result in production rate, egg size, feed efficiency, fertility, the extinction of the line within a few genera- hatchability, viability, disease resistance, body tions. This is a particular concern in lines propa- size and shape, and behavioral characteristics. gated by full-sib matings which also have large To change the population mean for one or more genetic loads (many deleterious alleles). How- of these quantitative traits requires rigorous ever, once the lethal and sub-vital alleles have testing and ranking of the individuals and family been purged from the inbred strain, it can theo- groups for the traits-of-interest each generation, retically be bred to essentially complete homozy- followed by selective breeding of the higher- gosity while maintaining reasonable reproductive ranked individuals and families to produce the performance traits (fertility, egg hatchability, egg next generation. Many factors can affect the rate production rates, viability, etc.). Such genetically of improvement in response to selection includ- uniform stocks can then be used as a standard ing 1) degree of heritability of the trait or traits genetic background in the study of individual involved, 2) selection stringency, 3) level of in- genes and gene complexes. Par- ticularly useful inbred lines are Box 7. Highly inbred stocks in immunogenetics those which have been bred for contrasting phenotypes due to BASIC INFORMATION ABOUT FACTORS control- including coccidiosis, Newcastle’s dis- allelic differences at single loci. ling disease resistance in the chicken ease, and the tumor-inducing viruses These lines, having the same has been gathered largely from stud- that cause Marek’s disease and lym- ies with congenic strains of chickens phoid leukosis. The congenic MHC genetic background for practi- (birds with identical, highly inbred strains, most requiring at least ten gen- cally all loci except for the alle- backgrounds but different major his- erations of back-crossing and blood- les of interest, are called tocompatibility complex (MHC) testing to develop, are key resources congenic lines. They are used to haplotypes; ABPLANALP 1992). A num- required for furthering our understand- study single-gene effects on pro- ber of these congenic strains have been ing of the way the MHC genes func- ductivity, for molecular charac- developed at the University of Califor- tion. Studies with these stocks have al- nia–Davis, the USDA Avian Disease and ready given the primary poultry breed- terization of genes affecting de- Oncology Laboratory in East Lansing, ers vital information to use in deter- velopmental traits or disease MI, the University of New Hampshire, mining the best of several alternative resistance, and many other uses and Iowa State University. Researchers breeding strategies to enhance disease in basic biological and biomedi- have shown how each MHC-haplotype resis-tance potential of their produc- cal research (ABPLANALP 1992). could directly affect the resistance of tion stocks. a bird to a variety of different diseases,

9 breeding, and 4) genetic variation in the original DNA, usually containing a gene of interest, into source population. Selected stocks usually re- one of the chromosomes of germline or somatic quire several generations to develop, tend to re- cells. While some transgenic chickens have been vert towards the original stock values if the se- produced in the past few years (SALTER et al. lection pressure is lifted (i.e., if random or non- 1986; 1987; SALTER and CRITTENDEN 1989), the selected pedigree reproduction is used), and creation of transgenics is still very much experi- usually need to be reproduced in large numbers mental in chickens and other avian species. (several hundred birds) each generation for the However, a number of research groups continue best selection differential with minimized in- to develop and refine transgenic methodologies, breeding. and report promising advances in the production of transgenic birds (SALTER et al. 1987; LOVE et Mutant stocks incorporate one or more of the al. 1994; THORAVAL et al. 1995; MARUYAMA et al. many single-gene mutations that have a major 1998). effect on specific morphological or physiological traits. These include variants (alleles) that affect Research genetic stocks eggshell color, feather color or shape, skin color, comb shape, metabolic function, major histo- Genetic stocks are used in three areas of re- compatibility complex (MHC) haplotype identity, search: agricultural, biomedical, and basic or and pattern formation in the developing embryo. fundamental biological research. The wide array of mutations affecting feather Agriculturally important avian genetic stocks color and shape are important for distinguishing primarily include those selected for various pro- between breeds and varieties within breeds. In duction-related characteristics (egg production, the poultry industry, eggshell color, skin color, body shape, feed-use efficiency, leg strength, dis- feather color, and feathering rate mutations, ease resistance). Another use for such stocks is and, more recently, MHC types, have all played to provide a flexible, rapidly responding model important roles in the development of commer- system for testing breeding techniques and sys- cial strains and varieties. Of particular interest tems that might also be useful with large live- to biomedical researchers are those mutations stock species (e.g., pigs, sheep, and cattle). These that cause disease conditions that mimic human stocks are particularly vulnerable to funding genetic disorders, including muscular dystrophy, cuts due to the long development period needed scoliosis, scleroderma, and a variety of develop- for most selected stocks, and the relatively large mental mutations (usually lethal) that affect the numbers that must be produced and monitored development of the face, limbs, integument, and annually to produce the selected population. internal organs. Biomedical research specifically uses animal Cytogenetic variants are birds that have chro- models for the study of various human diseases. mosomal abnormalities, such as aneuploidy, Avian models, mostly in the chicken, exist for polyploidy, translocations, and large insertions the autoimmune forms of vitiligo, scleroderma, or deletions. A small number have been estab- and thyroiditis, as well as for various develop- lished in the chicken, and these have provided mental defects, such as polydactyly, scoliosis, useful model systems for the study of meiosis, and cleft palate. Genetic stocks are also used in inheritance, recombination, linkage, transcrip- avian health research for studying the nature of tional regulation, and gene dos- age effects. Such stocks include: aneuploidy for the chro- Box 8. Chicken chromosome rearrangement stocks mosome encoding the MHC and nucleolar organizer region FROM THE MID-1960S TO THE 1980s, ani- the sex chromosomes, and sources of mal genetics laboratories at Ohio State aneuploids). Unfortunately, with the (NOR), complete triploidy (three University, the University of Minnesota, lack of support by various agencies copies, instead of two, of all and New Mexico State University de- over the last ten years, over thirty of chromosomes), large deletions veloped about 40 different chromo- these unique genetic resources were (the mPNU line, in which there some rearrangement strains in the irretrievably lost. The seven still in ex- is segregation of an MHC/NOR chicken (ZARTMAN 1971; WOOSTER et al. istence, along with a recently isolated chromosome with a deleted 1977; WANG et al. 1982). A number of spontaneous translocation, are cur- studies by these laboratories made im- rently being maintained at the Univer- NOR), and various stocks carry- portant contributions to our under- sity of Wisconsin. However, with de- ing translocations between standing of chromosome behavior in partmental reorganizations and bud- macrochromosomes (Box 8). avian species (including recombination, getary difficulties, these stocks are also Transgenic stocks are chromosome segregation, identifica- threatened. formed by inserting foreign tion of pseudoautosomal regions on

10 disease resistance and effects of specific genes mercial importance, such as the sex-linked gene on productivity under disease stresses. controling the rate of feather growth that has Most of the genetic stocks are of value for been heavily utilized by modern chicken breed- studying questions in basic biology that may ers (Box 9). lead to more applied biomedical or agricultural In marked contrast to the general perception research, or by simply contributing to the knowl- that commercial poultry stocks all have a rela- edge of how different biological systems function tively small and diminishing genetic base, some in a wide variety of studies in the life sciences. researchers have reported the opposite. Specifi- Some of the specialized stocks have been cally, DUNNINGTON et al. (1994) used DNA finger- derived directly from commercial chicken, tur- printing to measure variability among commer- key, or Japanese quail lines, while others were cial chicken breeding populations and concluded developed from special breeds, landraces, or that a considerable reservoir of genetic diversity wild-types. yet remained. IRAQI et al. (1991) reported a great degree of polymorphism for endogenous viral (ev) Commercial stocks genes in five egg-type populations maintained by an Israeli commercial breeder. AARTS et al. (1991) The commercial poultry stocks have made re- also found variation for ev genes among and markable genetic progress in the last 50 years within six WL and four medium-heavy brown (Boxes 9, 10, and 11). At this time, selected eggshell lines. While none of these methods spe- stocks used in commercial egg or meat produc- cifically reflects the variation remaining in genes tion must fit very specialized production criteria. associated with economically important traits, To develop these criteria, each breeding company the recent substantial progress in the develop- has identified particular commercial goals (egg ment of the genetic map of the chicken (CHENG et production, weight gain, feed conversion, carcass al. 1995; CHENG 1997) should soon lead to more characteristics, etc.) and seeks to meet them in thorough and realistic assessment of the amount the shortest possible time (EMSLEY 1993). In this of economic trait variability remaining in com- way, the fundamental difference between basic mercial poultry populations. and applied research is highlighted. While a researcher may have a preferred outcome for an Fancy breeds and mid-level experiment, any result can provide useful information to that researcher or others in the reproduction stocks search community. For the commercial breeder, the only outcome that is acceptable is one that For at least 50 years, poultry fanciers have been improves the commercial product for the con- the main conservators of the majority of the sumer, and increases final prof- itability for the producer (HUNTON 1990). Box 9. Economics of sex-linked genes and chicken genetics From a commercial production point of view, the loss of IN 1908, SPILLMAN REPORTED that the fe- chicks are all fast feathering. Such unique avian germplasm has a male was the heterogametic sex in chicks can be easily sexed at hatch time chickens (now described as ZW, as com- by the relative feather growth by any- number of negative repercus- pared to mammals where the male is one with a minimum of training. Previ- sions. To start with, production heterogametic, XY). This was based on ously chicks were sexed using the vent objectives and economic stan- the finding that the barring gene was sexing method, whereby rudimentary dards are constantly changing, inherited as a sex-linked gene, being copulatory organs were examined to particularly for meat production passed from the dam to her sons. This determine sex. This was a costly pro- birds. This means that agro- early finding has played an important cedure, and at $0.03 per chick would role in commercial poultry breeding, cost a hatchery $3,000 for every nomic industries will continue as many lines are now sexed at hatch 100,000 chicks hatched. Over 600 mil- to need access to genetic diver- time using the sex-linked rate-of-feath- lion egg-type chicks are hatched an- sity to meet future market de- ering gene. This gene influences de- nually in the US. If only half of these mands, to adapt to adverse en- velopment of the early wing feathers are sexed by feather sexing, the vironmental conditions, to fight in the chick. If the dam carries the slow chicken industry saves over $9 million new diseases, and to meet the feathering mutation, K, she passes this per year. Broiler breeders are incorpo- on to all her sons, and her W chromo- rating this gene also, as sex-separate demands for different nutri- some to her daughters. If the sire is rearing becomes more prevalent. With tional values. Thus, an effort pure for the wild type gene, k+, all the over 9 billion broilers hatched in the must be made to identify and daughters receive the wild type fast- US each year, this also will have an eco- conserve all useful genetic re- feathering gene. The male chicks are nomic advantage to the industry. sources that could have com- all slow feathering and the female

11 poultry breeds and varieties in North America, aspects to this practice: small parcels of land particularly the old dual-purpose or mid-level can remain agriculturally productive; open space production breeds (Box 12). As the Leghorn is maintained, family farmers are aided; and chicken, Rock-Cornish cross chicken, and moneys go into the local economy. broad-breasted Large White turkey became the Biomedical researchers are starting to be- dominant commercial birds, commercial breed- come aware of the genetic reservoir available in ers could see no economic benefit to maintaining the fancy breeds. They usually seek specific other standard breeds and varieties of poultry standard breeds or feather patterns that can be recognized by the American Poultry Association used in exploring biological questions (see Chap- (APA 1998). Today, without fanciers, it would be ter 3) or problems related to human medical dis- very hard to find an Ancona or Silkie chicken or orders, e.g., a form of vitiligo in barred chickens a Royal Palm turkey. The Lamona chicken breed, (BOWERS et al. 1994). The Silkie breed (Figure 9) developed by the USDA, is a notable American is particularly useful, with six dominant muta- example of a once-useful old-fashioned produc- tions: crest (Cr), rosecomb (R), muffs-and-beard tion strain now fallen from favor. (Mb), polydactyly (Po), ptilopody (Pt), fibromel- In some cases, access to mid-level stocks can anosis (Fm); and one recessive mutation, hook- help small-scale producers stay in business. less (h). These mutant alleles produce: elongated While they cannot compete with the Rock-Cor- feathers on the crown of the head (Cr) and on nish meat cross or Leghorn egg-layer in the the face and chin (Mb), a broad, flattened comb highly commercial marketplaces, they can be- that is covered with small, fleshy nodules (R), come financially successful by raising some of extra toes (Po), feathered legs and feet (Pt), dark these heirloom birds to supply specialized niche skin, bones, and viscera (Fm), and loose, excep- markets (Box 12). There are many other positive tionally fluffy body feathers (h). Not only have

Box 10. Development of egg-laying stocks

COMMERCIAL EGG-LAYING chickens (Figure 1940s and 1950s was primarily due to 90% of all the egg-type chickens in 6) have shown a substantial increase the introduction of hybrid stock, utiliz- North America, and probably well over in productivity in the past 60 years. ing pure breeds which had been under half of the commercial egg-type chick- Some of this improvement has been development by numerous small breed- ens worldwide. due to developments in the areas of ers participating in the National Poultry Crosses among lines of the White management, nutrition, and disease Improvement Plan (NPIP). The more re- Leghorn (WL) breed produce nearly all control, but the effect of genetic im- cent increase has been primarily due to the commercially marketed white-shell provement is clear (ARTHUR 1986). Be- selection for increased egg numbers. chicken eggs in North America. The WL tween 1940 and 1955, the number of However, it should be remembered that lines in use today stem from the pure- eggs laid per hen in the United States the work of the small breeders and the bred stocks sold in the 1930s and increased from 134 to 192 (USDA-NASS formal testing parameters set by NPIP 1940s. Though there has been inter- 1998). By 1994, eggs per hen had in- shaped the foundation stocks, paving the crossing in many cases to develop new creased to 254. The change in the way for the phenomenal performance in strains, many of the currently used the modern commercial stocks appear to have been selected birds. without intermixing for 30 years or Today, only a few large more. Of particular note is the com- international poultry mon use of the Mount Hope strain, breeding companies pro- which is distinguishable by its large duce most of the world’s egg size and the B-19 and B-21 major commercial egg-type histocompatibility complex blood types chickens. Just 40 years which it carries (for an explanation of ago, the 1958-59 sum- the major histocompatibility complex mary of US random- (MHC) and B-blood types, see the sec- sample-egg-production tion on Immunogenetics in Chapter 3). tests (ARS 1960) listed In response to regional consumer 132 breeding firms. In the preferences, several commercial most recent egg-layer test brown-eggshell chicken lines have also still conducted in North been developed. Typically less efficient America, (NORTH CAROLINA than the White Leghorn strains, com- COOPERATIVE EXTENSION SER- mercial brown-eggshell chicken lines VICE 1996) only five breed- are usually produced by crossing ing companies were listed. Rhode Island Red males with high pro- These were actually duction White Leghorn females. Alter- Figure 6. White Leghorn hen (Photo courtesy owned by just three inter- natively, some high egg production national firms. These strains of Rhode Island Red or Barred of U.K. Abbott, University of California–Davis). three firms breed over Plymouth Rock may be used.

12 the hobby breeders helped in supplying such the hobby breeders and the different breed orga- research birds for one-time projects, but some of nizations, a number of problems are associated them have participated in long-term breeding with their conservation: 1) most of the amateur programs for researchers. conservators often only keep their stocks for a Although the majority of exhibition and mid- short period of time (typically just five years); level production poultry breeds have continued 2) small-scale hobby breeders who get breeding to exist under the rather informal stewardship of stock from a central clearing house of poultry

Box 11. Development of meat-producing stocks

IN 1950, A COMMERCIAL BROILER took 84 sumer ideal. The broiler-breeders were of the dual-purpose breeds. The out- days to grow to 1800 grams; by 1970, fortunate to have available the Cornish bred or crossbred parents have better this was cut to 59 days, and by 1988, breed (derived from fighting stock im- reproductive traits and general vigor it was down to 43 days (from HUNTON ported from India), which had many of than parents from the pure-lines, and 1990). As with the egg-type chickens, the desired carcass characteristics. The their offspring, a three- or four-way a large proportion of the improved per- breeders also found that the production cross, exhibit even more hybrid vigor. formance of meat birds can be attrib- characteristics (body type, rate of gain, Unfortunately, despite careful evalua- uted to developments in the areas of feed conversion) improved rapidly in re- tion of the breeding stock, some seri- management, nutrition, and disease sponse to selection. Unfortunately, im- ous structural and physiological prob- control. But choice of foundation provement in these areas had a strong lems have surfaced that appear to be breeding stock and early use of breed negative effect on the already poor re- the result of the intense selection for crosses were also important in the de- production characteristics of the Cornish desirable production characteristics. velopment of the broiler industry. lines (low egg production, low fertility, These include: leg weakness, cardio- More so than the egg market, the poor hatchability, reduced chick viabil- pulmonary insufficiency, breast blis- broiler market is strongly consumer- ity), and seriously impaired disease re- ters, increased fat deposition, and driven (POLLOCK 1999). Early consumer sistance (see section on immunogenet- muscle anomalies. input (chicken of tomorrow competi- ics, Chapter 3). The early breeders found While the turkey industry is consid- tions between 1946 and 1948) gave that crossing the Cornish roosters with erably smaller than the broiler chicken the broiler-breeders and growers a hens from improved dual purpose breeds industry, many of the same breeding good picture of consumer preferences: solved many of these problems. These methods have been used, and many compact, well-fleshed carcasses at af- “female” line breeds, including the Ply- of the same problems have been en- fordable prices. In other words, the mouth Rock and New Hampshire, have countered (HUNTON 1990). With a scrawny, angular cockerels (Figure 7) better body type than Single-comb White smaller genetic base, and a much available in large numbers from egg- Leghorns, yet lay eggs at a relatively high larger bird to start with (Figure 8), the selected Single-comb White Leghorn rate compared to the Cornish “male” structural and physiological problems lines did not even approach the con- lines. Today, the commercial sire is of- found in chickens are often magnified ten a cross between two in turkeys. Considering the small num- predominantly Cornish ber of primary breeders (three) and the strains, and the commer- scarcity of exhibition or research tur- cial dam is a cross be- key breeding stock, it is imperative to tween two strains de- safeguard the remaining genetic diver- scended from one or more sity of this domestic species.

Figure 7. Traditional broiler-type chicken Figure 8. Commercial Large White turkey tom (Photo cour- carcass of the 1940s (Photo courtesy of F.A. tesy of R.A. Ernst, University of California–Davis). Bradley, University of California–Davis).

13 stocks may never know their egg source or the degree of relationship of their foundation stock; 3) breeding populations are often very small, particularly for the rarer breeds, and pedigree information is frequently limited or not available; 4) some hobbyists deliberately inter-cross different breeds or varieties in attempts to improve or modify exhibition traits; 5) selection for production characteristics (e.g., fertility, viability, egg production, or disease resistance) may be largely ignored in these small-scale breeding programs, although de facto natural selection will tend to eliminate the infertile, disease-susceptible, or least-viable individuals; and 6) backyard breeders tend to have problems in controlling diseases Figure 9. Silkie rooster from UCD Silkie (Photo cour- and may have serious endemic diseases. If there tesy of J. Clark, University of California–Davis). were a formal conservation pro- gram for avian genetic resour- Box 12. Small renaissance of old-style chicken breeds ces, it would be logical for it to provide technical services to WITH THE INCREASING CULTURAL diversity ers are getting their stocks from the of our population, the white-feathered, few people who still maintain popula- these hobbyists who are a very highly selected meat- or egg-produc- tions of true Rhode Island Reds, Speck- important component of avian ing bird no longer meets the needs of led Sussex, New Hampshires, and so genetic resources conservation. all consumers. In response to a great on. Those supplying the specialty egg demand by ethnic markets and the markets are also looking for different many upscale restaurants searching for breeds to produce a colored egg that the “chicken of yesterday”, more and will be distinctive (brown, tan, green, more small producers are starting to or blue), such as Orpington, Rhode Is- raise “old fashioned” mid-level produc- land Red, and Ameraucana. Unfortu- tion or dual purpose breeds (those that nately, most of these so-called mid- are reasonably efficient at producing level production breeds have all but both meat and eggs). These produc- disappeared from American farms.