Embryo manipulation in cattle breeding and production

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Abstract
Developments, both recent and potential, in procedures for manipulating embryos are described. The procedures considered include: embryo transfer, multiple ovulation and embryo recovery, recovery of oocytes,in vitromaturation (IVM) and fertilization (IVF) of oocytes,in vitroculture of zygotes, embryo splitting and nuclear transfer, embryo storage, embryo sexing, gene transfer and embryo stem cells. The impact of these procedures on breeding strategies such as multiple ovulation and embryo transfer (MOET) nucleus breeding schemes and progeny testing are discussed for both dairy and beef cattle.For MOET nucleus schemes all these procedures have potential applications in producing maximal rates of genetic progress for a fixed rate of inbreeding. With the current effectiveness of the procedures, embryo sexing and nuclear transfer would have the most impact. The potential for increasing genetic progress through progeny testing is enhanced using multiple ovulation, embryo recovery and transfer in cows to breed bulls, but no other procedures appeared to offer major benefits. The efficiency of beef production from the dairy herd could be increased either by using IVM and IVF to produce more beef-type calves or, potentially, by cloning and embryo transfer, to produce pure beef calves. Procedures leading to the production of clone families would make an impact on the evaluation of genotypes and environments. Gene transfer may be used to modify the composition of milk including the production of pharmaceutical proteins, and to increase milk yield or the efficiency of lean meat production.It is concluded that, although much further research is required, the procedures discussed will have major implications for the structure and organization of dairy and beef cattle herds over the next decade.