Sheep - AgRIS
Sheep - AgRIS Sheep - AgRIS
Oral administration of L-thyroxine to Suffolk sheep brought about an increase in wool production per unit area of skin due to an increase in fiber length growth rate and also caused an increase in milk secretion during the second to eighth week of lactation in Black Leicester X Scotch Black face ewes. The main glucocorticoid secreted by the adrenal cortex of the sheep is cortisol and the plasma level of cortisol in the sheep is exceptionally low compared to other species. Administration of cortisol or ACTH to normal sheep suppresses wool growth and complete inhibition can be produced even though the plasma cortisol level remains below that of other species for which the plasma levels are known. Raised levels of plasma cortisol cause "breaks and "tenderness" of fleece. Stress conditions such as injury, disease, starvation and extremes of environmental temperature stimulates adrenal cortical secretion and a break in the fleece following such conditions is probably medicated via the adrenal cortex. Growth hormone having direct action, does not appear to have a permissive effect on wool growth in that it does not permit growth in hypophysectomized sheep, more over it does supplement the response to thyroid hormone in the sheep. Other pituitary hormones such as prolactin, gonadotrophic hormones or oxytocin do not appear to have any significant permissive or regulatory effect on wool. e) Physiological state It has significant effect on wool growth. In general entire males produce more wool than castrated males which produce more than females. There is no real evidence, however, to suggest that these differences are determined by anything other than differences in size and nutritional state. The reproductive cycle in females can reduce wool growth significantly. During late pregnancy, depression of wool growth rate in the range of 20-40 percent has been found and even in breeds which exhibit a marked seasonal depression, pregnancy can depress the rate still further. In lactating ewes, wool growth is also reduced by upto 30 percent or more, despite the accepted increase in voluntary intake associated with lactation. The average reduction in clean fleece weight between handicapped animals (twins and progeny of young ewes) and unhandicapped (singles and the progeny of adults) animals born in the same year was 150 g. The period most sensitive to nutrition deficit is from 30 days before to 35 days after birth (Fraser, 1954). f) Age Rate of wool production in most breeds increases to a maximum between four and five years and then declines, often rapidly. g) Nutrition The most important factor affecting adult wool growth however, is the current level of nutrition (Fraser, 1954; Kapoor et al., 1972) . Increase in energy intake, except at very low levels of protein content in the diet, can have an immediate effect on wool growth detectable within a few days. It is generally accepted that wool growth rate is dependent on energy rather than protein intake. Wool protein contains a high proportion of the high sulphur amino acid, cystine, and it has been shown that variation in the availability of the sulphur amino acids to the follicle can affect both fiber growth rate and fiber composition. It is not possible to estimate the actual amount of energy which produces wool. The amount of metabolizable energy which is drawn upon for wool production is likely to exceed materialy the combus tible energy for wool fiber and of the secretions which accompany it, which is 3% of the metabolizable energy derived from rations (Marston, 1955). Deficiency of minerals such as calcium and vitamin D are associated with depressed wool growth. These act indirectly possibly by affecting health and appetite. Carbohydrate supplementation to sheep increases body weight and fleece weight (Fraser, 1954). The addition of carbohydrate to diet converts a negative nitrogen balance into a positive one (Krishnan, 1939). Carbohydrate is necessary for mitosis to take place and there is importance of glycogen in the follicle for wool growth. 12.2.2 Genetic There is variation in wool production in various breeds. In five wool breeds, winter growth rate has been found to be around 85% of that in summer, whereas in British hill breeds the winter rate may be as low as 30% of that in summer. The wool quality of Deccani and their 467
crosses with Dorset and Merinos, Patanwadi and Deccani crosses has been studied by Daflapurkar et al. (1979) and Deshpande and Sakhre (1987). The importance of differences between strains and probably breeds of sheep is indicated by recent work with merinos indicating small but significant differences in efficiency of conversion of feed to wool. The behavioural differences between individual sheep subjected to competition for limited feed, are another source of variation. Feeding groups of sheep once per week gave higher mean body weights and fleece weights than feeding them equal amounts on daily basis. Difference of social order within a flock or group of sheep also determines wool production. 12.3 Wool Quality The Sheep farmers/ producer of wool should have a working knowledge of the wool quality. They should be able to determine the value of the wool raised so as to look out for their own interests. Otherwise they will find themselves at the mercy of the wool buyers at market time. The various factors that are taken into account for judging the quality of wool are: 12.3.1 Fiber Fineness The diameter or thickness of wool varies. The thinner and finer the fibers, the more valuable is the wool. The unit for measurement of thickness is a micron or 1/10,000 of a centimeter. The wool fiber has a diameter varying from 12 to 80 microns. Fine wools range from 15 to 25 microns in diameter. The fleeces obtained from the merino breed are of this quality. 12.3.2 Length of Fibers stable The length of the fiber is important in determining the use that may be made of it in manufacture. Long wool is more valuable than x short wool. 12.3.3 Medullation A true wool fiber has no stiffcentral core in it. As a rule, the finer the wool and more elastic and uniform the fibers are, the better it is considered for spinning purposes. Apart from its being of a fine type, it is of utmost importance that throughout the fleece, there should be as much uniformity as possible in the fineness of the fibers. There should also be uniforrnity in the diameter of the individual fiber so that each one is even throughout its entire length. Wools from improved breeds do not show variations in excess of 50 per cent from the finest to the coarsest, while in the case of unimproved sheep, the coarsest fiber may be 5 or 6 times as thick as the fine ones. 12.3.4 Crimp or Curliness of Fibers Wool, as it grows on sheep, develops a wavy structure which is called the crimpiness. In fine wools, these curls are larger in number and more regular in a unit-length of fiber than in coarse fleeces. Crimp is often emphasized by some as being a very important feature of wool. The number of crimp per inch is usually associated with fineness of fiber, but this is not necessarily always the case. Wool fineness cannot be judged on the basis of crimp alone. Some Australian wool has a "bold" crimp but is finer than other wool that has a closer crimp. Crimp is related to elasticity and some other features, but its chief value is probably in the fact that an even, distinct crimp indicates a well-grown, sound fiber of uniform diameter and length. The other features of good wool are enhanced and made more evident by such crimpiness. 12.3.5 Strength of Fibers The stronger the fibers and the less they break, the higher is the quality of the wool. Strength is another matter that influences the value of wool. Strong, durable fabrics can be made only from wool that is well grown and sound. The strength or soundness of the wool fibers is largely dependent upon the health and nutrition of animals. Certain other environmental factors may affect the strength of the fibers. Sheep that remain in good health and that have regular nourishment, both with respect to quality and amount, are able to maintain a uniform growth of fiber and hence have sound fleeces. If the nourishment is suddenly reduced or radically changed so as to affect the health of the sheep, the fibers are 468
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crosses with Dorset and Merinos, Patanwadi and Deccani crosses has been studied by<br />
Daflapurkar et al. (1979) and Deshpande and Sakhre (1987).<br />
The importance of differences between strains and probably breeds of sheep is indicated by<br />
recent work with merinos indicating small but significant differences in efficiency of<br />
conversion of feed to wool.<br />
The behavioural differences between individual sheep subjected to competition for limited<br />
feed, are another source of variation. Feeding groups of sheep once per week gave higher mean<br />
body weights and fleece weights than feeding them equal amounts on daily basis. Difference of<br />
social order within a flock or group of sheep also determines wool production.<br />
12.3 Wool Quality<br />
The <strong>Sheep</strong> farmers/ producer of wool should have a working knowledge of the wool<br />
quality. They should be able to determine the value of the wool raised so as to look out for their<br />
own interests. Otherwise they will find themselves at the mercy of the wool buyers at market<br />
time.<br />
The various factors that are taken into account for judging the quality of wool are:<br />
12.3.1 Fiber Fineness<br />
The diameter or thickness of wool varies. The thinner and finer the fibers, the more<br />
valuable is the wool. The unit for measurement of thickness is a micron or 1/10,000 of a<br />
centimeter. The wool fiber has a diameter varying from 12 to 80 microns. Fine wools range<br />
from 15 to 25 microns in diameter. The fleeces obtained from the merino breed are of this<br />
quality.<br />
12.3.2 Length of Fibers stable<br />
The length of the fiber is important in determining the use that may be made of it in<br />
manufacture. Long wool is more valuable than x short wool.<br />
12.3.3 Medullation<br />
A true wool fiber has no stiffcentral core in it. As a rule, the finer the wool and more<br />
elastic and uniform the fibers are, the better it is considered for spinning purposes. Apart from<br />
its being of a fine type, it is of utmost importance that throughout the fleece, there should be as<br />
much uniformity as possible in the fineness of the fibers. There should also be uniforrnity in the<br />
diameter of the individual fiber so that each one is even throughout its entire length. Wools<br />
from improved breeds do not show variations in excess of 50 per cent from the finest to the<br />
coarsest, while in the case of unimproved sheep, the coarsest fiber may be 5 or 6 times as thick<br />
as the fine ones.<br />
12.3.4 Crimp or Curliness of Fibers<br />
Wool, as it grows on sheep, develops a wavy structure which is called the crimpiness. In<br />
fine wools, these curls are larger in number and more regular in a unit-length of fiber than in<br />
coarse fleeces.<br />
Crimp is often emphasized by some as being a very important feature of wool. The number<br />
of crimp per inch is usually associated with fineness of fiber, but this is not necessarily always<br />
the case. Wool fineness cannot be judged on the basis of crimp alone. Some Australian wool<br />
has a "bold" crimp but is finer than other wool that has a closer crimp. Crimp is related to<br />
elasticity and some other features, but its chief value is probably in the fact that an even,<br />
distinct crimp indicates a well-grown, sound fiber of uniform diameter and length. The other<br />
features of good wool are enhanced and made more evident by such crimpiness.<br />
12.3.5 Strength of Fibers<br />
The stronger the fibers and the less they break, the higher is the quality of the wool.<br />
Strength is another matter that influences the value of wool. Strong, durable fabrics can be<br />
made only from wool that is well grown and sound. The strength or soundness of the wool<br />
fibers is largely dependent upon the health and nutrition of animals. Certain other<br />
environmental factors may affect the strength of the fibers. <strong>Sheep</strong> that remain in good health<br />
and that have regular nourishment, both with respect to quality and amount, are able to<br />
maintain a uniform growth of fiber and hence have sound fleeces. If the nourishment is<br />
suddenly reduced or radically changed so as to affect the health of the sheep, the fibers are<br />
468
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