Current developments in the genetics of livestock improvement.

There is a character in a play of Molitre who was pleased and surprised to be informed that he had been speaking prose all his life. Most 1ive;tock producers are in somewhat the same position: without being aware of the fine body of genetic theory which exists, they have nevertheless been steadily putting in into practice for many centuries. What then has the science of genetics to add to the efforts of practical 1ive;tock breeders? In the first place, it provides a rational basis for their activities and obcervations. Hence breeders need not speculate about whether the stallion or the mare has the greater genetic influence on the offspring the genetic mechanism ensures that their contributions are approximately equal. Cattle breeders need not devote a generation of activity to stamping out an undesirable recessive gene its recessiveness guarantees its persistence, though at low frequency. The decline in fertility and viability which often accompanies inbreeding can be explained largely as the effect of increasing homozygosity in exposing such recessive genes. Secondly, it provides a verifiable starting point for the development of the complex breeding operations that many populations now require, and that are as far removed from simple selection as the motor car is from the bicycle. Example; are the large and complicated breeding and selection programmes that produce modern egg-laying chicken strains, or the large investment which is currently made in testing and selection of dairy cattle for use through AI. Inevitably, much of the contribution of genetics is simply to provide the hard physical base on which investment appraisal can be carried out, and one of the more active areas in the genetics of livestock improvement is precisely this region, where genetic events meet their economic consequences. How adequate is genetic theory, as it now stands, for this role? Where are the major deficiencies? How can it be made more useful as a basis for the practical decisionmaking that constitutes an animal improvement programme?