SHEEP AND GOATS

New Zealand Herald, Volume LXXIV, Issue 22896, 26 November 1937, Page 5

SHEEP AND GOATS

MINOR DIFFERENCES DISTINGUISHING FEATURES RESULTS OF EVOLUTION

BY H.B.T

Because of their value in yielding milk, meat, skins suitable for clothing, and gut and sinews for the manufacture of weapons, sheep and goats were probably among the earliest animal species domesticated by man. But possibly because of our very familiarity with them, few naturalists have made an exhaustive study of the sheep's features. The differences between the sheep and the goat are not great. They were both, naturally or originally, found chiefly on high uplands and mountains and, apparently, came from the same parent stock, which slowly evolved into many species of antelopes, mouflon, goats and sheep. ]n many wild species tho two latter are only quickly distinguishable by tho fact that the goat's tail is carried erect, like most deer or antelope, while tho sheep's is pendant. It is possible, however, that this obvious difference is largol.v the result of selective mating under domestication. Tho Interdigital Pit

Tho chief distinguishing feature between goats and sheep is that the latter have a small pit or opening from a gland, known as the "interdigital pit," situated between tho claws of tho hoof. This secretes an oily fluid which apparently lubricates the surfaces between the claws and may also have been of value to wild sheep as a scent sac, producing a distinguishing odour, which enabled tho various members of the flock to follow their leader to a rendezvous when they had been scattered by predatory animals. We have all seen ewes separated from their lambs, or even from their usual mates in the flock, follow this scent confidently for miles.

Why this interdigital pit should be necessary, or even an advantage to sheep and some species of antelope, and not to goats and cattle is obscure. It is noticeable, however, that if this orifice becomes blocked with dust or inud, "scald" immediately occurs, and this inflamed condition favours the establishment of tho germ which causes footrot. Whereas browsing animals such as goats and cattle can stand a considerable amount of wet underfoot, sheep and other grazers (mostly having the interdigital pit) must have dry ground. Nature's Pasture Cultivators

The divided or "cloven" hoof common to many herbivorous animals has a real value apart from the secure footing which it provides the beasts on the steep and slippery faces which they naturally frequent. These sharp, pointed and edged hooves effectively cultivate the sward, aiding in preventing it from becoming turf-bound and facilitating the entry to the soil of air and moisture. At the same time they lightly consolidate the actual surface soil, and thus encourage the establishment and survival of the shallow-rooted grasses upon which this species is principally dependent for its food. The sheep's highly nitrogenous manure also favours the growth of surface-rooting grasses, hence they vastly benefit the type of growth which, in turn, is best suited to maintain them. Deductions from the Eyes

Another feature of sheep which is of •onsidorable importance, and yet is very infrequently discussed, is the position and other peculiarities of the eyes. In carnivorous animals the eyes are se,t to the front of the head for, situated thus, they are of most service in discovering their prey. The eyes, also, are not prominent or long sighted, and their pupils contract, leaving u vertical slit or oval. This gives them their widest range of vision above, below and straight in front of them. The herbivorous 'animals have their eyes placed more to the sides of their heads, and the eye sockets usually project to greater or less degree, giving the animal a range of vision to each side and behind, as well as in front. The field of vision in front is not so good as is that to the sides, and for that reason the wild, herbivorous animals always lie with their heads up-wind to scent danger approaching from that direction, and all of them also rest with the head held fairlv high, and back on the neck, so as to have an unrestricted view behind. This gives the "ewe-necked" appearance common to wild sheep and most of the deer, antelope and goat species. The prominent eyes sot to the sides of the head enabled these animals to see approaching enemies from any direction, and gave them the opportunity of escape "up-wind." l'he pupils of their eyes also contract horizontally, thus giving them the wide, level range of vision necessary to their safety even in daylight. At night, when these herbivorous animals naturally graze, the pupils of the eyes are widely dilated, giving them comparatively good vision in dim light when we, for instance, would he unable to see. The Origin of Prepotency

The further to the sides, and the more prominent the eyes of these wild, herbivorous animals were, the wider their range of vision and the more likely thoy were to escape their enemies. Thus the individual animals with the widest foreheads and most prominent eyes survived and became the heads of their flocks and herds, not only because they had more brain capacity, but because they could see further and more quickly than their fellows. Vigour and courage also played their part in ensuring survival and so, in course of time, sheep and cattle with prominent eyes, broad foreheads and courageous, virile characteristics became dominant. Through long mating of like to like, and the rigorous culling b.v natural agencies of those which did not develop these characteristics in high degree, these animals became extremely " prepotent." That is, they were able to pass on their most important characteristics to their progeny and submerge, or "dominate," weakness of the same features in their mates. Thus, when we find a ram with great width between prominent eyes, we are certain that this will be accompanied by a bold and rather aggressive carriage. Hut more important still, we know that he will be prepotent: that ho will reproduce his own typo, whether good or bad, in his progeny. All prepotent animals are, of course, not necessarily good in the. features which man desires for production, but when the valuable characteristics are found combined with decided indications of prepotency, that animal is invaluable to the breeder. With him ho can establish and fix a type having prepotency, virility and valuable production in one or two years which might otherwise take him a lifetime to achieve, if ever his goal was attained. It can be seen, therefore, that a study of these minor features of sheep of which there are many besides those discussed here —may prove of the greatest practical value to the sheepman, for in many cases these characteristics may reveal an important hereditary weakness or strength linked with the survival of the type from the dim past.