Metabolic and endocrine differences between Bos taurus and Bos indicus females that impact the interaction of nutrition with reproduction.

During the last decade, researchers have studied the differences in the reproductive physiology between Bos taurus and Bos indicus breeds. This manuscript focuses on the main aspects of ovarian function and circulating hormones of B. taurus and B. indicus cows and heifers. In general, there is no difference in the number of follicle waves during the estrous cycle, however B. indicus have greater antral follicle count, circulating insulin, and insulin-like growth factor 1 (IGF1) than B. taurus. Moreover, despite of B. taurus having larger ovulatory follicle diameter and maximum CL volume, they have lesser peak circulating estradiol concentrations and lesser circulating progesterone concentrations than B. indicus. We may speculate that there are two main factors related to lesser circulating concentrations of estradiol and progesterone in B. taurus when compared with B. indicus: increased liver metabolism of steroid hormones and lesser production by follicles and CL. Differences between the two genetic groups are also observed with respect to in vitro embryo production because in addition to B. indicus having greater numbers of retrieved oocytes, due to greater antral follicle count, they also have greater percentages of viable oocytes, number of blastocysts, and blastocyst rates when compared with B. taurus. Effects of dietary intake on embryo quality may differ between B. taurus and B. indicus due to different concentrations of circulating insulin and IGF1. For in vivo and in vitro embryo production, an increase in circulating insulin concentrations is negatively associated with oocyte/embryo quality and conception rates. However, this seems to be more pronounced in B. taurus breeds. Differences in ovarian function related or not to nutrition between these two genetic groups are very consistent and may be related to the influence of metabolic hormones such as insulin and IGF1.