Integration of transgenes in breeding programs

Abstract

ABSTRACTConventional animal breeding is in a healthy state, with good rates of genetic change possible, and economic efficiency being continually improved in the different livestock species. New reproductive techniques offer faster rates of change, as with the use of embryo transfer in sheep and cattle breeding. It is now possible to introduce foreign DNA, transgenes, into the germ line of farm animals and this offers new opportunities in the genetic improvement of economic merit. The transgenes should be directed at traits of high economic value, and be made in elite breeding stocks to benefit from past genetic improvements. Much still needs to be learned about engineering transgenes and about the basic biochemical-physiological processes they are designed to affect. However many transgenes will be produced over the next decade, and some may be useful in animal improvement. Founder transgene individuals are unique for incorporation site, copy number and expression, and will require screening, multiplication, testing and evaluation, in both hemizygous (TO) and homozygous (TT) form, for all economic traits. For a transgene with a large useful net effect on economic merit, the most rapid genetic response will come from fixing it in the elite breeding stock. An effect of 5-10 percent in economic merit will be needed to offset the normal genetic improvement displaced. Current experience with transgenes is of very large effects on the target trait, but with deleterious effects on fitness and economic merit. Control of the level, tissue and time of expression are crucial to the practical use of transgenes. With uncertainty in the results of a transgenic program, conventional programs will have to be maintained, so extra investment will be required. Patent rights may bring extra benefits to breeders, but there are also risks if the stock prove defective. Breeding strategies and organization may also change. Despite initial problems and uncertainties, the power of the transgenic methods is so great that the development of transgenic stocks is likely to become a very important tool in genetic improvement of livestock in the future.