No abstract

Currently, timed ovulation induction and fixed-time artificial insemination (FTAI) in superstimulated donors and synchronization protocols for fixed-time embryo transfer (FTET) in recipients can be performed using GnRH or estradiol plus progesterone/progestin (P4)-releasing devices and prostaglandin F(2α) (PGF2α). The control of follicular wave emergence and ovulation at predetermined times, without estrus detection, has facilitated donor and recipient management. However, because Bos taurus cows have subtle differences in their reproductive physiology compared with Bos indicus cattle, one cannot assume that similar responses will be achieved. The present review will focus on the importance of orchestrating donor and recipient management to assure better logistics of procedures to achieve more desirable results with embryo collection and transfer. In addition, this will provide clear evidence that the use of FTAI in superstimulated donors and FTET in embryo recipients eliminates the need to detect estrus with satisfactory results. These self-appointed programs reduce labor and animal handling, facilitating the use of embryo transfer in beef and dairy cattle.

No abstract

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.