Breed Standards - Sussex Cattle Breeders Society

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and the second is that even after the population stood still at a selection limit for a considerable period of time, it reacts immediately on reversed selection in the vast majority of cases, In other words, the genetic variation is also not exhausted noteably by selection. Variety is Normal The first principle that we should understand, therefore, is that the animal breeder is busy manipulating a highly variable genetic pool. The second major principle to remember is that the primary function of sexual reproduction is in fact to maintain this generic variation. No two individuals in a sexually reproductive population appear or are alike – no two people, sheep, horses or whatever. Each fly on the windowpane has it’s own face like every human being has his or her own face. They only appear alike to us, just like the animals of a stud breeder will appear like to the inexperienced city dweller. Avoid In-breeding At last we can accept, after half a century’s controlled matings of affinities, that species which normally reproduce sexually , retrogress with inbreeding and that even strong selection pressure has barely any influences in counteracting this retrogression (Pircher, 1969). Even with poultry, where it is possible for in-breeding to take place much faster than with bigger farm animals, Stephenson and his coworkers came to the conclusion that “strong in-breeding can decrease 16 performance much more effectively that selection can increase it. Therefore it hardly seems economical to produce inbred lines for commercial use” (Stephenson et al. 1953). The success stories which in practice are frequently attributed to in-breeding on closer investigation, usually appear to be more likely due to selection. Against this background, namely the extent of variation that is present, sexual reproduction, the unity of the genotype and in-breeding retrogression a few remarks on a number of aspects of breeding in practice, are relevant. Firstly avoid in-breeding. Why follow a mating system which even in the vegetable kingdom, nature goes out of its way to avoid? Don’t take the botanist as an example. His situation is totally different because he can, for example, self-fertilize maize, he can reach a degree of in-breeding which would take 40 years of parent-onprogeny or full blood brother on full blood sister with farm animals. The botanist normally does at least 5 generations of self-fertilization before he starts crossing. Also remember that the approximately 60 inbred maize lines used for the reproduction of hybrid maize in the USA towards 1950, were selected from about 100 000 original inbred lines. Selection the Key to Success Selection remains the most powerful method to change the genetic composition of the population. Often, however, selection takes place exactly with the view to stabilizing the population average at an intermediate optimum (for example fibre diameter in the case of Merino’s). This type of
selection has three results: naturally it decreases the variation of the present population, but it has no notable effect on the variation of the next generation and it prevents a change of the average. More often, however, selection is aimed at a higher or lower value, for example for bigger or smaller animals. This results in displacement of the population averages, but again the variation is seldom notably influenced. The differences between the best and the poorest remain about the same, but both groups continue to improve. It is simply not possible to get all the animals of a large stude to be equally as good. Inherently they differ from each other and for this very reason sexually reproductive populations ar so pliable and therefore susceptible to selection. For this reason the Simmentaler in Germany could be selected as a dual purposed breed, while the same breed is primarily a beef breed in Australia. There are no short cut magic formulas to change the genetic composition of a breed overnight (except, of course, through crossbreeding with another breed). It is a question of continuous selection pressure with a firm objective in mind. One or two percent progress in a year is the best one can hope for in the majority of cases. This is why it is so important to limit mistakes to the minimum. Firstly, and perhaps most important, with regard to objectives, but of course also as far as selection itself is concerned. 17 Objectives One of the most difficult aspects in animal breeding is to formulate clearly outlined breeding objectives. Consider the changing needs of the market; the diversity of conditions in which the same breed must produce the lack of knowledge on exactly what the breed originally looked like; and where one’s physiological limits are, then one can understand why breeding objectives are vaguely formulated in terms of breed standards. <strong>Breed</strong> standards, in the case of older breeds, are in many respects a description of the breeding progress already achieved. One should expect in these cases that breed societies should rather entertain the view that the vast majority of their animals conform to the breed standards at any rate, and that the differences that do occur are very natural and will always be there if the population reproduces sexually (in contract with, for example, cloning). Instead of being possessed by ideas of breed standards, such a bred society should incessantly propagate the strong aspects of its own breed, while the breeder asks himself: in respect of which traits should my breed be improved further, and selection should then be aimed primarily at those traits. The major function of the stud breeder is to provide bulls to the conventional producer. The bulls that he provides should, however, possess certain characteristics and it is firstly important for the breeder to formulate these characteristics clearly for himself and then strive for them consistently. When establishing objectives, three factors should be borne in mind: the objectives
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Breed Standards - Sussex Cattle Breeders Society

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