BREEDING OF LIVESTOCK

New Zealand Herald, Volume LXXII, Issue 22047, 1 March 1935, Page 15

BREEDING OF LIVESTOCK

EVOLUTIONARY PROCESS FOLLOWING NATURE'S LEAD IMPROVEMENTS IN TYPE BY H.B.T. No. V. The process of evolution toward superior types is accomplished by Nature through at least three processes of selection. In the first instance there is "preferential mating " that is, superior types of males prefer to mate with females having similar, qualities, and will neglect inferior individuals. This instinctive selection is very evident to those who have closely studied wild life. The second method is "gametic selection." I believe, for instance, that in an experiment in which Ayrshire cows were first of all put to a Galloway bull before they were served by an Ayrshire, all the calves are said to have been pure Ayrshire. Influence on Wool Environmental selection is the third medium through which evolution works. Just as in the colder climate of Northern Europe and Asia the sheep species developed a dense undercoat of wool, so in the tropics, the speoes having no need of this development, the whole coat became coarser, longer and more open, being well designed to turn tropical storms, protect the sheep from rough undergrowth, and at the same time admit air freely to the skin and facilitate transpiration. The environment of each type decided the lines along which variations or mutations should take place.

The adage that "like begets like" is only partly true. There is always a tendency to variation. No two animals are identical. The nearest approach to exact reproduction is in cases of selffertilisation, which takes place among various lower forms such as snails, or in cases of reproduction by simple division, as in still lowlier forms such as the tape worm. Such types are stationary, or very nearly so, on the evolutionary ladder, for advance in evolution can only take place when advantageous variations frequently occur.

While, with some few exceptions, sports and reversions are to be avoided in so far as domesticated livestock is concerned, variations must be taken advantage of when they obviously better fit the animal to its environment, or increase its productiveness. Possibilities ol In-breeding It has been stated that reversions occur most frequently when the crossing of distinct breeds is undertaken, and especially when these are derived from differing original types. On the other hand, slight variations which permit of steady improvement occur when the breed is selected and mated within itself. Most rapid improvement of all is undoubtedly achieved when the selections and matings are within one particular family or "line" of blood, for then desirable characteristics can be depended upon to blend, and the features are built upon and intensified until the animal becomes prepotent, or dominant, in respect of them. Ihis is Nature's main method of securing evolutionary advance, and, provided the precautions which she herself employs are adopted, there seems to be no way in which her method can be improved. But there is no reason why animals may not become prepotent in respect to bad as well as good qualities. If one were to mate animals having the same weakness, that weakness would be intensified as surely and quickly as would any desirable quality. As closely related animals are likely to have inherited similar weaknesses, there is a distinct danger of such matings. Health in Natural Conditions Under natural conditions the bulk of animals enjoy perfect health, and have through many generations acquired perfect adaptation to their environment. Should too closely related and weakly animals mate, their progeny would be so enfeebled through the intensification of faults as to be unable to survive. Under conditions of domestication, however, these sickly specimens may be so protected and nursed that they frequently survive. If mated with related stock having similar weaknesses, the result is disaster in the progeny. On the other hand, such weakly stock, if mated to a vigorous reversion, or with unrelated animals having strength where they are weak, the progeny may possess normal health.

The trouble with which the breeder is faced in conducting in-brceding is that he may have difficulty in detecting incipont weaknesses in the stock with which he is working, and which, when intensified, become disastrous defects. When such a condition exists, an outcross likely to correct the weakness is the only possible remedy; the outcross in this instance being one of blood or family only, and not of breed. As the control point of the animal's whole system is definitely the head, and as it is also the medium through which all nourishment enters the system, we would expect to see deliniated in it evidences of the animal's health, as well as its prepotency. A bright, intelligent eye, capacious nostrils, a wide, wellformcd mouth, and ample room for food and air passages between the jawbones and where the throat joins the head are infallible signs that the animal has all the appurtenances to perfect physical health. Prepotency and Type Animals in-bred for even eight or ten generations acquire prepotency in a marked degree, as well as uniformity or "type." It is questionable whether the same improvement could he secured by any other method of breeding in ten times the period unless a "sport" arose and was used to advantage. Many mistakes, however, have been made by using this method, the most common being the development of some desirable characteristic at the expense of some other feature, which thus becomes n weakness. In other words, "balance" is lost. As a preliminary to the improvement of any particular feature, it is necessary to improve either the quality or quantity of the animal's food, or to increase its. capacity or power of assimilation. Given perfect health as a foundation, and a steadily increasing capacity to assimilate nourishing food, rapid improvement in production can be achieved through persistent and intelligent inbreeding.