NEW TECHNOLOGIES TO IMPROVE THE REPRODUCTIVE EFFICIENCY OF DAIRY-CATTLE

The genetic potential of Canadian dairy livestock has improved conside rably during the past 25 years, due mainly to a massive increase in th e use of artificial insemination and embryo transfer. As a result of r ecent developments in reproductive biotechnology, a marked improvement in the efficient use of artificial insemination and embryo transfer c an soon be expected. For example, the synchronization of follicular wa ves has greatly improved the precision of oestrus synchronization prog rams, reduced and even eliminated the need for oestrus detection, and allowed fixed-time artificial insemination. The efficiency of embryo p roduction, both in terms of the number of embryos produced and monitor ing of production-related operations, has also been improved by contro lling ovarian follicular dominance. Major advances have been made in t he in vitro production of embryos as a result of transvaginal ultrasou nd-guided aspiration of oocytes, and the discovery of the effect of fo llicular status on oocyte quality and competence for embryonic develop ment. Refinement of molecular biology tools related to increased avail ability of high quality cattle embryos has favoured the emergence of s creening and transgenesis techniques. Thus, it is possible to know the sex of the embryo before its transfer by carrying out a molecular ana lysis of a biopsy using a specific Y chromosome-probe. The same type o f approach is currently applied to detect animal carriers of the AA, B E and AB alleles for the kappa casein gene. Subjects who are carriers of BE alleles not only produce mote proteins but also a larger proport ion of caseins. Finally, although slowed down by technical pitfalls, t ransgenesis applied to cattle leads us to consider applications aimed at an increased synthesis of caseins, a reduction of lactose and the p roduction of human proteins in milk. Taken together, the application o f the new reproductive biotechnologies will lead to a decrease in the generation interval, which in turn will greatly accelerate genetic adv ances.