Follicular development, superovulation and artificial insemination in embryo donor cattle

Abstract

Although significant advances have been made in embryo transplant technology, embryo transplant units still have to cope on a daily basis with persisting hurdles. One of these problems relates to superovulation methodology that results in consistent ova production within and across donor cows. Although research publications on the subject date back over 30 years, this problem remains as an annual topic of discussion at the professional and embryo transfer society meetings. It has now become painfully clear that our basic knowledge of primordial follicle activation, follicle recruitment, follicle receptor site interactions, endocrine involvement in follicular development and follicular growth dynamics is less than adequate. There is a need for research to develop workable physiological models so that we can better understand follicular growth and development.

A second problem relates to the artificial insemination (AI) of donor females to produce optimal fertilization rates across embryo collections. With thousands of donor cows superovulated and inseminated in the world over three years, it would seem that this problem should have been resolved by now, but unfortunately variability in fertilization rates and low viable embryo recovery still exists. These results suggest that basic research is also needed on oocyte maturation and fertilization before additional progress can be made in this area. It now appears that research efforts should focus on developing and understanding of how these physiological events occur in situ rather than conducting repetitive field trials hoping to uncover optimal superovulation and insemination schedules for donors in commericial embryo transplantation programs. It is agreed that this type of physiology research is often difficult, time consuming and costly. It has now become evident that a renewed effort is needed in basic research before further progress is made in harvesting the optimal number of transferable quality embryos from each donor female.