Bovine embryo production : what are the future research options for increasing the efficiency of superovulation treatments ?

Abstract

In bovines, commercial development of embryo transfer has existed for about 15 years. Despite the number of studies undertaken during this period, two major initial problems remain unsolved. The first is that there are still, on average, only a low number of embryos harvested from each treated cow. This, consequently elevates the production cost. The second problem is the large number of animals that do not produce any transferable embryo, making the use of this technique less attractive in genetic improvement programmes. These problems limit the development of the embryo transfer technique. They go on, despite the fact that the superovulation treatments have been optimized, and that the hypophysial extracts used to stimulate follicular growth are better defined and controlled than they were 15 years ago.

At the moment, the main factor determining the number of transferable embryos is the number of induced ovulations. Studies investigating the relationship between ovarian function and the response to superovulation treatments have demonstrated that the number of ovulations depends on the status of the follicle population at the beginning of the gonadotropic stimulation (presence of a dominant follicle, number of follicles greater than 2 mm in diameter). It seems, therefore, that improvements in the efficiency of the superovulation treatments depend less on the development and use of new molecules or new protocolsof treatment than on the administration of a "pre-treatment" capable of causing the dominant follicle to regress and/or augmenting the number of follicles that could be recruited by the gonadotrophins. To this end, several possibilities are understudy. The initial results are encouraging and should soon allow new strategies to be proposed that will produce embryos more efficiently.