Sheep - AgRIS

staple length and the fiber length of a fleece. Fiber length is measured by stretching sufficiently
to remove the crimp. Crimp may account for as much as one-third of the total length.
Much study of the size and shape of wool fibers has been made by means of various types
of projection apparatus at both low and high magnifications. For some kinds of physical
studies, this apparatus is well suited. Other apparatus has been developed for the study of
length, strength, pliability, and so on.
Wool fibers are seldom circular in cross-section. Most of them are irregular-shaped when
viewed under a microscope or when projected onto a screen after being cross-sectioned. In
studies of many wool samples at various wool laboratories, the general variations in the shape
of the fibers and in their size have been universally noted. Fleeces sometimes show extreme
differences in these respects, and none have been found that are completely uniform, even
though the fibers are from a ver,y rvricted area of the skin.
According to many, the wool fiber is hollow, and it is through this channel that the fiber is
nourished by various "juices." There appears to be no basis for such statements, for once the
fiber has been elaborated it is not further changed by any activity of the body. The yolk does
serve to keep it in good condition, but this is in no sense a nourishing of the fiber. The fibers
have no nerves or blood supply in them. There is also a common belief that dyes enter the wool
fibers through the channel which is supposed to pass from end to end. This is not the case, as
fibers are readily dyed in the center without immersing either end into the dye.
The chemical composition of wool is complex, and it is possible that there is considerable
variation, depending upon the type of wool. The physical properties of wool are undoubtedly
related to its chemical structure. Pure wool is composed of keratin, which is also the
chiefoonstituent of hair, feathers, horns, and hooves. Keratin is closely related in composition
to some of the proteins, but it is not identical with them, as the keratin of wool is not, at least,
readily digestible in gastric juices as many proteins are. It is probable that much of the material
of which the wool fiber is composed is derived from the proteins in the feeds, but these are
changed in the elaboration of the fibers. Studies hf e shown that sheep on a ration of alfalfa
have deposited 6.8 kg protein daily in the production of the fleece for each 454 kg live weight.
While wool is represented as composed chiefly of keratin, cystine is represented as the
main constituent of keratin. It is in cystine that sulphur is present in wool. The sulphur content
of clean wool is about 3.4 per cent. Cystine occurs to a greater or lesser extent in most protein
foodstuffs and is an essential in body growth This has ed to the investigation of the significance
of sulphur in the diet, and its relation to wool quality and to wool growth. If sulphur is essential
to wool production, then a deficiency would lead to a reduced weight of fleece if the percentage
of sulphur was maintained, or it would lead to an abnormal fleece if the weight of fleece was
maintained. Since keratin has a constant percentage of sulphur, investigators expected no
change in chemical composition of wool as a result of feeding increased amounts of cystine.
Slight increases in weight and slight though noticeable differences in some features of wool
(glossiness) have been reported as a result of such feeding.
The content of cystine in wool is exceptionally high. studies have shown that the cystine
content of the proteins of plants is less than the cystine content of wool (13.1 per cent of the dry
wool fiber). Since it is unlikely that animals can manufacture cystine, their only source is that
contained in their feed. To produce 450 g of wool protein, a sheep must eat at least 3.2 kg of
vegetable protein. It seems probable that, from a practical standpoint, cystine may be in the
same category as many other substances: namely, a certain liberal allowance is needed for
normal production; a deficiency reduces production; an excess does not stimulate production to
such an extent as to cover the increased cost of such feeding.
Since sulphur is found in wool, there have been recommendations that sulphur, even
though not in the form of cystine, may be the limiting factor in wool growth. The feeding of
inorganic sulphur has, however, not been found to have any tendency to influence wool growth.
Certain of the other minerals are also found in the ash of wool after it is burned. These are
present in very minute amounts, and it is possible that rations that are adequate for the general
nourishment of sheep are also adequate for maximum wool growth. While there may be a
measurable difference through the use of delicate laboratory apparatus in the amount of wool
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