THE ROLE OF EMBRYO TRANSFER IN CATTLE IMPROVEMENT PROGRAMS

Abstract

Embryo transfer has added a new dimension to animal reproduction and breeding. It is now possible to obtain up to 40 offspring from a selected female in 1 yr. Originally all transfers were done surgically; however, recently, non-surgical embryo recovery has been highly successful. Future developments are required for equal success in non-surgical implantation. The problems in embryo transfer rest with unreliable superovulation, fertilization, embryo and recipient identification. Pregnant mare serum gonadotrophin has shown considerable variation as a superovulating agent when administered to embryo transfer donors with the use of prostaglandin F2α as a leuteolytic agent. Sources of variation in donor and recipient females are discussed, including egg quality, timing of transfer and the use of surgical and non-surgical transfer procedures. With the use of optimal conditions it should be possible to obtain an average of approximately eight pregnancies per successful donor. The role of embryo transfer in beef, dual purpose and dairy improvement programs is discussed. Embryo transfer is currently being used for the expansion of limited gene pools whereas in the future such transfers will be for the successful proliferation of offspring from the mating of genetically superior dams and sires. A doubling of response can be obtained in beef improvement programs where defined objectives can be identified.