Associations of antral follicle count with fertility in cattle: A review.

Ovarian antral follicle count (AFC) is a marker of ovarian stimulatory response to superovulation protocols in cattle. This article reviews novel research from the past 10 years, focusing on the relationship between AFC and embryo production and cow fertility. Substantial evidence indicates a positive relationship between AFC with embryo production; however, conflicting findings exist regarding the relationship of AFC with conception and pregnancy rates. This lack of consistent association with pregnancy outcomes is perplexing given the differences detected in oocytes, embryos, and endometria from high- versus low-AFC animals. Those differences include markers of embryonic viability such as protein level, blastocyst development rates, cleavage rates, and blastocyst cell numbers that differ between high- and low-AFC groups, as well as differential gene expression at the cow and embryo level with genes associated with fertility. In addition, and cattle appear to have different fertility responses based on their AFC category. In summary, clearly more studies are needed to elucidate the true associations between AFC and cow fertility, but the data that have been accumulated thus far indicate that AFC has the potential to be a useful marker of lifetime cow fertility.