New technologies to improve the reproductive efficiency of dairy cattle

The genetic potential of Canadian dairy livestock has improved considerably during the past 25 years, due mainly to a massive increase in the use of artificial insemination and embryo transfer. As a result of recent developments in reproductive biotechnology, a marked improvement in the efficient use of artificial insemination and embryo transfer can soon be expected. For example, the synchronization of follicular waves has greatly improved the precision of oestrus synchronization programs, reduced and even eliminated the need for oestrus detection, and allowed fixed-time artificial insemination. The efficiency of embryo production, both in terms of the number of embryos produced and monitoring of production-related operations, has also been improved by controlling ovarian follicular dominance. Major advances have been made in the in vitro production of embryos as a result of transvaginal ultrasound-guided aspiration of oocytes, and the discovery of the effect of follicular status on oocyte quality and competence for embryonic development. Refinement of molecular biology tools related to increased availability of high quality cattle embryos has favoured the emergence of screening and transgenesis techniques. Thus, it is possible to know the sex of the embryo before its transfer by carrying out a molecular analysis of a biopsy using a specific Y chromosome-probe. The same type of approach is currently applied to detect animal carriers of the AA, BE and AB alleles for the kappa casein gene. Subjects who are carriers of BE alleles not only produce mote proteins but also a larger proportion of caseins. Finally, although slowed down by technical pitfalls, transgenesis applied to cattle leads us to consider applications aimed at an increased synthesis of caseins, a reduction of lactose and the production of human proteins in milk. Taken together, the application of the new reproductive biotechnologies will lead to a decrease in the generation interval, which in turn will greatly accelerate genetic advances.