The potential role of molecular genetic manipulation in the improvement of reproductive performance

Revolutionary opportunities for the modification of animal performance are being created by the development of new methods for embryo manipulation and the application of molecular biology. This paper reviews the potential application of these procedures for the improvement of reproductive performance in livestock. There are three sections: a consideration of the methods of molecular manipulation that are available at present and those that seem likely to become available, a discussion of the modifications to hormonal systems and, finally, an analysis of candidate genes for manipulation of seasonality, number of ovulations, sex ratio and prenatal survival. The analysis points to a number of ways forward. Many of the most promising opportunities will depend upon the isolation of embryonic stem cells or the establishment of alternative methods of site-directed mutation. In most cases, the genes of interest have not yet been cloned and much remains to be learned about the molecular regulation of reproduction. A greater understanding seems likely to reveal the inadequacies of some of the present suggestions, but it is also certain to reveal further opportunities. However, in the longer term, there seems to be a real prospect of modification of at least some of these aspects of reproductive performance by molecular means.