The Relation of Nutrition to the Production of Hides

THE RELATION OF NUTRITION TO THE

PRODUCTION OF HIDES AND WOOL

by John I. Hardy and Imogene P. Earle ^

I n t K t is no doubt that nutrition affects hides and wool, but research has been too Umited to give any detailed results. In summarizing the existing information, this article shows definitely that the level of feeding of sheep greatly influences both the quantity and the quality of the wool produced.

THE MANY USES of animal skins and their associated fibers—wool, liaiij and fur—make the production and quality of these materials important in the economics of essential commodities. However, except in those few enterprises specifically devoted to the production of furs, animal skins are more often than otherwise only byproducts of other industries, and the production of animal fibers, even in the sheep industry, is frequently secondary to the production of meat. Rela- tively few studies have been devoted primarily to the factors influencing production and quality of skin compared with the large amount of research on the production of animals for meat. More attention has been given to the production of animal fibers, especially as repre- sented by the wool of sheep, and considerable progress has been made in this field. Breeding, nutrition, climate, sex, age, and management of the animals all probably influence the growth of skin and its associated fibers—wool, hair, and fur. Fraser (389) ^ has pointed out in a review of the influence of nutrition on wool that ''the maximum quantity and optimum quality of wool grown by sheep is determined by its genetic constitution,^' and that ''the importance of nutrition lies in the pro- vision of concrete materials for the full expression of genetic potential- ities.'^ This generalization probably applies to the production of other animal fibers and of skins as well. So far as is known, nutritive factors affecting the production of hide and hair are either dietary deficiencies or the factors that correct dietary deficiencies. It is believed that the amount and quality of body covering of an animal cannot be increased

1 John T. Hardy is Senior Animal Husbandman, Animal Husbandry Iîvision, and Imogene P. Earle is Associate Biochemist, Animal >iutrition Division, Bureau of Animal Industry. 2 Italic numbers in parentheses refer to Literature Cited, p. 1075. 492 HIDES AND WOOL 493 through change in the diet beyond the level resulting from a diet that supplies in adequate amounts all the dietary essentials for maintenance, growth, and reproduction. An improvement in quality beyond that attained on an optimum ration for health must be the'result of changes in genetic factors or possibly in external environment. On the other hand, the kind and quantity of hide and hair produced modify the nutritive requirements of the animal. STRUCTURE OF SKIN AND WOOL A brief consideration of the nature and structure of skin and wool may lead to a better understanding of the role of nutrition in their production. Skins of all mammals are anatomically and physiologically similar. Leather may be made from them all, although there is a wide range in the texture of the product obtained. Skins in their raw state consist of three layers, the epidermis or thin outside layer, a second thicker layer known as the corium, and a third layer of adipose tissue or flesh. In the process of tanning, the first and third layers are removed. The epidermis is made up of cells—an underlay er of living epithelial cells and an outer layer of dead cells. This outer layer consists mostly of an insoluble protein, keratin, and affords surface protection to the body. As these outer cells are lost they are replaced by the under layer of living cells. The epidermis has no blood vessels of its own and must obtain its nourishment from the blood and lymph supplied by the blood vessels of the corium. The corium is made up of interlacing connective-tissue bundles, elastic fibers, and smooth muscle fibers. The texture of the corium nearest to the epidermis is finer and the connective-tissue bundles are more closely interwoven, while the deeper portion nearest to the adipose tissue is more coarsely meshed. The fine-textured portion is recognized as the papillary layer and the coarser textured part as the reticular layer. It is the upper papillary portion that makes the grain in leather. Wool, hair, and other animal fibers grow from cavities (follicles) that surround them. The wool fibers are first visible to the naked eye as they push up from the follicle throagh the minute recesses of the skin. The actual growth of a wool fiber takes place at the papilla in the bulb at its lowest extremity. The root ends of the fiber extend to varying depths in the skin. The cells formed at the papilla are pushed upward by the formation of new cells and become keratin- ized, or hardened, before they appear above the skin. Associated with the wool follicles are the sebaceous or fat-secreting glands, which provide oil to lubricate the fiber. There are also the sudoriferous glands, which exiide sweat and suint. The excretions of these two kinds of glands form what is known as the yolk in a fleece of wool. Pure wool substance is essential^ a structure made of the protein keratin. This protein constitutes the major substance of hoof, nail, and hair and is present to a lesser extent in the cells of the upper layer of the epidermis. There are apparently many keratins differing somewhat in composition according to the structure in which they are found, the species and color of animal, and other factors, including the nutrition of the animal. All keratins are characterized by a high 494 YEARBOOK OF AGRICULTURE, 1939 content of the sulfur-containino* amino acid, cystine. Keratins differ from other proteins chiefly in their insolubility in neutral solvents and in their high sulfur content. Hides also consist chiefly of protein ; because of the complexity of their structure they are made up of a number of different proteins. FACTORS INFLUENCING HIDE QUALITY According to Tänzer (1121) both thickness and quality of hides— and consequently of leather—are inffuenced by sex^ age, breed, management, and environment of the animals producing the skins, and in the case of sheep, by the amount of wool grown on the hide. Fur- ther, there is considerable variation in the hide from one part of the animal to a.notlier. The larger animals grow thicker hides, and the skin on the main body of the hide is thicker than that foimd on the head, neck, and legs. The skin is also thicker on the back than on the belly. Tougher skin is found on and near the shank, owing to the sparseness of hair and the mechanical activity of this portion of the animal. Bulls have thick ludes, but the leather is soft and is held to tear more readily than that made from cows and steers, which have smooth, strong, elastic skin. Rams have thicker and ffrmer skin than ewês and wethers. Leather from young animals is softer and lighter in weight than that from older ones. Generally speaking, heavily wooled sheep seem to have thick, spongy skins. The skin of Merinos, for example, is thicker than that of wild sheep. Both cold and highly variable warmer climates are believed to cause the production of tJiick skin. Mountain range cattle, for instance, have coarser skins than those of lower altitudes that are fed in barns. That nutrition also aff'ects the thickness and quality of hide has been demonstrated by the work of Clark, Stuart, and Frey {213), who made a comparative study of the hides of full-fed and underfed lambs. In this study iiine lamb wethers on full feed received a daity ration of 1.20 pounds of grain, 0.60 pound of corn silage, and 1.01 pounds of clover hay, while their twin brothers received an ''under feed^' daily ration, of 0.22 pound of grain, 0.59 pound of corn silage, and O.oH pound of clover hay. The feeding test lasted for 112 days^ during which the full-fed lambs nearly doubled their weight while the weight of the underfed lambs j-emained practically the same throughout the feeding period. The final average body weight of the full-fed lambs was 88.7 pounds and that of the underfed lambs 49.9 pounds, and the weight of the whole skins was 7.888 and 3.72 pounds respectively. Grain, reticular layer, and whole skins all averaged thicker for the fiül-fed group (fig. 1). The finished leather in the full-fed group aAêraged 0.046 inch and that in the underfed group 0.026 inch in thickness. The leather of tlie full-fed group averaged much stronger and had a greater tear resistance and a greater stretch at the point of rupture, but the strength of cross sections of equal area was approximately the same. The grain surface of the leather from the full-fed lambs was more developed than that of the underfed group, which was appreciably flatter. The most significant chemical difference in the skins was that those of the full-fed group contained a higher percentage of fat and also more cystine. Frey, Clarke, and Stuart (394) investigated the cause of fatty spots mo CO > Z

o O

Figure 1.—Cross sections of skins of iambs showing differences in development as a result of feeding: A, From full-fed lamb; B, from underfed lamb. X35.

■O 496 YEARBOOK OF AGRICULTURE, 1939 or "kidney grease" in heavy cattle hides and leather and found indi- cations that this defect may be associated with the increased fat content of hides from animals that have been on full food. EFFECT OF PLANE OF NUTRITION ON WOOL Nutritional research on animal fibers has been concerned almost wholly with the wool fibers produced by sheep. For over 100 years reported casual observations have indicated that gross weight and quality of wool can be influenced by nutrition factors occurring under natural feeding conditions. The production of a fine light fleece has been associated with light soils, strong harsh wool with limestone

Figure 2.—.\ weak spot in a staple of wool caused by serious nutritional tlislurhance. soil, and a characterless wool lacking in crimp with a heavy clay soil. Further, it has been said that the best quality of wool is grown in a country that produces short sweet grass, and that liberal feeding increases weight of fleece. E.xperimental evidence obtained from controlled feeding trials tends to support these popular beliefs. Tinley's observations (1138) indicated that lush pasture is associated with the production of a coarse, heavy fleece and sparse pastur- age with a finer grade of wool. There is ample proof in the literature that any combination of feeds that maintains sheep in good vigorous condition tends to produce a heavier fleece than rations that are less satisfactory' for maintaining general health and vigor. Wilson {1235) HIDES AND WOOL 497 compared the fleeces of sheep on a fattening ration with those of sheep kept on a submaintenance ration. The sheep on the fattening ration produced 343 percent more scoured wool, and it was 141 percent longer and 207 percent higher in breaking strength than that produced by sheep on the submaintenance ration. Results reported by Snell {1087) are somewhat similar in that he observed that sheep on a low plane of nutritioTi produced lighter, shorter, finer, and more crimpy wool than their mates that were receiving more feed (fig. 2). Snell also showed that a lower plane of nutrition may result in shed fleeces. It has been observed that when sheep have been improperly fed, even for a short time, and also in cases of disease, the fibers of the fleece often become reduced in diameter and as a result break easily (fig. 3). Such fleeces are said to be tender. When the ocmdition of

Figure 3.—A normal wool fiber contrasted with a weak broken one. malnutrition or disease continues for a protracted period, the fleece becomes so weakened that it is easily plucked from the skin. This condition is thought to result from any cause that results in low vitality or poor health. In some of the Southern States considerable difficulty is encountered in maintaining sufficient control over parasites to keep the sheep health}'. In such localities shed fleeces are not uncommon. Authorities are not agreed, however, as to the extent or limitations of the effect of plane of nutrition on quality and growth of wool. It appears that the change in fleece weight resulting from a lowered plane of nutrition is in general associated with a decrease in length and diameter of fiber. The fact that improved nutrition of the sheep results in an increased coarseness of wool has occasionally been considered a disadvantage, but the slight lowering in count is more than offset by the increased value of the fleece as a whole. 141894"—39 33 498 YEARBOOK OF AGRICULTURE, 19 39

ENERGY AND PROTEIN NEEDS FOR WOOL PRODUCTION The energy and total protein stored in the production of wool have been estimated by Mitchell, Kammlade, and Hamilton (801) in the course of a study of the utilization of a ration of alfalfa hay and corn by lambs. The}^ estimated that during the process of fattening, while body weight increased from 65 to 70 pounds to 90 pounds, the increase in amount of wool accounted for 8.S percent of the dry matter gained, 26.3 of the protein, 2.1 of the fat, and 5.2 percent of the energy. The daily wool growth of these lambs con tamed 0.086 pound of protein and 377 calories for each 1,000 pounds of live weight. These same investigators in an earlier experiment with mature sheep found a more rapid daily wool growth equivalent to the deposition of 0.149 pound of protein and 566 calories per 1,000 pounds of live weight. Since wool fiber is chiefly protein, the study of effect of nutrition on the production, of wool is especially concerned with the metabolism of protein and the conditions modifying it. Considerable work has been done to determine the effect of feeding high and low levels of protein. Results of such trials have sometimes seemed contradictory, but in general they tend to support the conclusion that the total protein requirements of sheep are not remarkably high in spite of the extra protein required for wool production, and that protein in excess of the requirement for maintenance and growth is apparently without effect on wool production. Marston (753) fed blood meal as a protein supplement to a large group of Merino ewes and lambs on the range and obtained a So- percent increase in clean fleece weight as compared with the group of controls receiving no blood meal. He attributed this increase to the content of the amino acid, cystine, in the protein of the blood meal. However, Fraser (389) has pointed out that these results are also open to the interpretation that the level of protein, rather than content of cystine, may have been the controlling influence, since Marston did not feed the control group a hke amount of protein poor in. cystine. Fraser and Roberts (391) were unable to show that wide variations in the protein level when other nutritional factors were kept constant caused any significant difference in wool charactersitics. It is believed, however, that the basal ration in this study contained sufficient protein to provide for both body growth and wool growth. CYSTINE REQUIREMENT Much of the research on the relation of nutrition to wool production has been directed in recent years to the role pla3êd by sulfur or sulfur-containing compounds in the growth of wool. Sulfur occurs in protein as one or both of the two sulfur-containing amino acids, cystine and methionine, and as inorganic sulfate. In the protein of wool or hair, most of the sulfur present is accounted for by the cystine, which constitutes approximately 13 percent of the keratin, whereas the proteins in animal and vegetable foods contain only 0.3 to 4 percent of cystine. For many years cystine has been considered indispensable for growth and health and incapable of being synthesized by the animal body from other substances. If it is assumed that cystine must be HIDES AND WOOL 499 supplied preformed in the food, a low^ level of protein in the pasture or other feed or protein low in cystine would seriously limit wool growth. It has been suggested that the capacity of any territory for carrying sheep is determined by the content of cystine in its pasture grasses. However, the requirements of sheep for preformed cystine have not been determined. Several workers have suggested that cystine is synthesized within the body of the sheep. Fraser and Roberts (391) estimated that the consumption of cystine was not sufficient to account for all that was laid down in the wool grown. They suggested that cystine was synthesized by the wool follicle. Rimington and Bekker (967) also calculated that the amount of cystine deposited in the wool of sheep during a year was more than was contained in all the pasture grass they could possibly have consumed. These workers suggested that cystine must be synthesized from proteins by bacteria in the rumen and intestine. Such conclusions^ however, are based on available analyses of the cystine content of pasture herbage and other feeds and are open to question because of the unreliability of methods used in the determination of cystine in feeds containing carbohydrate. Another line of investigation that may have an indirect bearing on the problem of the requirements of the sheep for preformed cystine deals with the relationship between cystine a]id methionine. Recently Rose (986) has shown, as a result of experiments with rats, that methionine rather than cystine is the indispensable factor. The inclusion of methionine in a cystine-free diet induced as rapid growth as the inclusion of both cystine and methionine. Cystine without methionine, however, was without effect, although cystine with a suboptimal quantity of methionine stimulated growth. Marston (754) studied the effect of administration of cystine, cysteine (a compound that yields cystine on oxidation), sulfur, and methionine on the growth of wool on a ewe receiving protein-poor rations. It had been found that on the basal ration alone ewes could maintain their weight and produce about 60 percent of the wool usually grown on pasture. Marston found that 1 gram of cystine added to the daily ration increased the growth of wool about 14 percent. Wool production was increased 34 percent when 1 gram of cysteine was injected daily, instead of being fed, to avoid destruction of the bacteria in the intestinal tract. The daily addition of 1 gram of sulfur to the ration was without effect. A small but not very significant increase in wool growth resulted from the daily injection of sufficient methionine to supply the same amount of sulfur as 0.5 gram of cysteine. This work indicates that cystine (or its derivative cysteine) is more readily available for the keratinization of wool protein than methionine and lends support to the idea that the feed is the chief source of wool cystine. EFFECT OF CARBOHYDRATE ON WOOL GROWTH Fraser and Nichols (890) have studied the relation of the carbohydrate content of the diet to wool growth and have shown that though wool is a protein structure it can be influenced by the carbohydrate in the diet. They fed a group of sheep on a balanced maintenance ration, half the sheep receiving 1 pound of maize daily in addition to the basal 500 YEARBOOK OF AGRICULTURE, 1939 ration. These animals had double the wool production of those not fed maize. The increase in weight of wool seemed to be chiefly due to the greater thiclovess of the indivichial wool fiber, This cfiêct was probably due to the fact that the readily available carbohydrate hi the maize could be used for energy and hence the available protein in the ration wâs utilized more efficiently for building and repair. OTHER NUTRITIONAL FACTORS Little work has been done on the specific efiect of the various uutri- tive factors other than proteins on the development of wool. Experi- ences in practical sheep raising have demonstrated, however, that well- fed animals have good fleeces and that many nutritional deficiencies interfere with the growth of wool. The importance of a sufficient supply of minerals in the diet has been recognized, and mineral deficiencies have been the subject of much research. There is no evidence that mineral deficiencies interfere with the growth of wool except as they aft'ect the general health of the animal. It has been observed that under circumstances that impose a phosphorus deficiency ou sheep there is a decrease in wool production. The evidence indicates, however, that the decrease in feed consumption induced by the phosphorus deficiency, and not a specific lack of the mineral, is responsible for the hiterference with wool growth. Correc- tion of phosphorus deficiency, therefore, serves to improve wool growth insofar as it increases the intake of proteiu, carbohydrate, and other nutritive elements. The results of work with laboratory animals in connection with the study of vitamins has shown that dietary deficienc}^ often causes a rough hide, a poorly developed coat, or even the loss of hair. A notable example is the dry, curly hair obtained by Hughes (ßöß) on pigs kept on diets deficient in vitamins of the B complex. With the knowledge that has been acquired from studies on small laboratory animals and on some kinds of livestock, a new field is UKU- cated for research on animal fibers and hides that should yield funda- mental information concerning their production. New techniques now being perfected for measuring quality in fibers and hides should greatly expedite such a program.