TYPES OF STOCK

New Zealand Herald, Volume LXIX, Issue 21247, 29 July 1932, Page 14

TYPES OF STOCK

/ CROSS-BRED ANIMALS RETROGRESSION IN EVOLUTION BY H.B.T. >) When man was given "dominion over tho beasts of the field " ho was not made only master of their !:;e and death. He must, necessarily also, accept responsibility for their health, physical well being, and evolution toward a higher type with a wider sphere of isefulness. In patriarchal times there were apparently only single types or breeds, but by a process of selection and breeding for obviously advantageous features, new and distinct breeds were evolved. Ihis process has been more or less continuous for Boine thousands of years, with the result that .we now haw numerous distinct varieties of every breed, each particularly suited to its environment and to some particular productive use Thus we have sheep bred exclusively to produce fine, medium or coarse wool, while in others •he wool has been practically neglected, ind perfection in the production of mutt<« (jii.vnt>**->•] -lpon. In cattle, horses, pigs, dogs and all other -'ome-tWorJ animals. the sani'- results of selection for particular services are obvious, and these types ale now so firmly established as to be distinct breeo.-, which produce progeny uniformly like themselves. • Selection has been tho method most successfully employed through the ages in producing new breeds, but every now nnd then, and particularly during the last two hundred years, breeders have attempted to hurry toward some goal of a new type, which they have set themselves, fiy crossing one breed with another. Tho instances where crossing has been successfully employed in the establishment of a new and better fixed breed, can be counted on the fingers of one hand. At the same time countless variations and improvements, practically amounting to the creation of new breeds, have been accomplished by selective breeding. Disapproval of Nature. That crossing between breeds, even wjien derived from a common stock, is in if approved by Nature as a desirable method in evolution, is indicated by the fact that slight variations in tlic gestation period either prevent conception, or where this takes place, as between the horse and donkey, produces a male which is incap cbls of breeding. One of the main evils of cross-breeding

is the reversion, to some common ancestral type, of a large proportion of the crossbred progeny. These we call " throwbacks." Take as a popular instance the Jesuits we have achieved through crossing the Lincoln and Romney Marsh sheep in the/ North Island Both admirable and valuable breeds of sheep in the particular environments for which they were evolved, they still have so many distinctive features or characteristics which are en ti'rely dissimilar, that it is almos! impossible to get a halfbred which is midway between the two. The original idea "i the cross was to get a sheep with the size and shape of the Lincoln combined wi!h the hardiness and mothering, or milking, qualities of the Romney; the weight arid lustre of the Lincoln fleece blenoed with the density, elasticity and spinning qualities of the Romney. /Actually, as the result of some thirty or forty years crossing, we have in most Romney-Lincoln Hocks specimens of every tvpe possible ranging between the two breeds. We have sheep with Romney bodies and Lincoln fleeces and vice versa (but, strange to say, practically no sheep that reach the ideal of the original breeders, combining the good qualities oi each breed and excluding the undesirable features.

Reversion in Type. As was to be expected in crossing two breeds so dissimilar in wool, there has been an immense amount of reversion, or throw-back, in this feature to a type - of covering which was common to the ancestors of both breeds. As every sheepman knows, the present fleece of wool ■with which our sheep are covered was, in the native sheep, a short undercoat through which long, straight, hairy fibres projected, forming a rough outer coat pro tectlne both the wool and the sheep from the effects of the weather. Through carefully mating together sheep having a predominance of wool over hair, or knup, as we call it. the hairy coat was ultimately eliminated and we had sheep carrying pure, unmed lllated wool. The follicle which once produced hairy, mednllated fibre, was now growing pure unmedullated wool, but when these two dissimilarly-woolled sheep were crossed, a retrogression occurred among many of the progeny, and medulla ted fibre again became distributed throughout the fleece. This is one of the chief faults which manufacturers complain of in our North Island wool to-day, and it is difficult to know how to rectify St wh°i!e we continue to favour crossbreeding. While we know that the polled, _ or hornless, state is a dominant, or original characteristic of cattle, it is questionable if it is so with sheep. One of the most curious results experie.i iid when these two hornless breeds the Lincoln and Homney, were first crossed, was the number of males which had horns. This applied also to the Leicester-Ronmey first cross, and occasioned the breeders considerable trouble in removing the threatened growths with caustic. This, apparently, was another instance of reversion to original types stimulated by cross breeding. Blend of Characteristics.

Cross-breeding to secure a blend of the desirable characteristics of both breeds, would be very much simplified could we thoroughly understand the effect of and unfailingly distinguish, " dominant and recessive " breed characteristics. The complexity of this subject can only be realised by those who have made an ex haustive study of genetics. Not only do breeds have general characteristics which are dominant or recessive as the case may be, but some individuals of each breed will be " prepotent "—a term used to describe an animal which produces progeny like itself, " dominating " the animal with which it is mated /Crossbreeding always introduces an in flirty of unexpecteJ problems, and even in the most capabl- breeder's hands is bound to result in the loss of the valuable single type, and in the creation of numerous unfixed types. Any advantages which could be srciired in the way of an improved typo or new breed, can lie as quickly and with far more certainty, achieved through selective breeding. Such methods of breed-improvement have also the immense advantage that the stock breed true to selected type, and a rever eion, or throw-back is most unusual. It would be possible to take selected pure-bred animals of either the Lincoln .or Romney breeds and without the intro diction of alien blood produce a fixed type corresponding very closely with an ideal Lincoln-Romney half bred. It might fcake some years to accomplish, but more remarkable breeding results have been •chieved-before, in many instances in less than a lifetime.