Information on Regulation of Reproductive Cyclicity in Cattle

Abstract

Reproductive cycles are regulated by hormones. The purpose of this paper is to give an overview of recent information on hormonal regulation of reproductive cycles in order to allow increased understanding of programs that are currently being developed or will be developed for improving reproductive efficiency in cattle.

Figure 1 shows a typical hormonal profile for 4 key reproductive hormones during the estrous cycle of the cow. Progesterone comes from the corpus luteum and increases after the time of ovulation and then decreases at the time of luteolysis. Prostaglandin (PG) F2a comes from the nonpregnant uterus and is the hormone responsible for luteolysis. AI, shown below PGF2a is secreted in distinct pulses near the time ofluteolysis. Estradiol-17B increases early in the cycle and after the time of luteolysis. This increase in estradiol causes estrus behaviour and the LH surge. The LH surge is responsible for ovulation of the preovulatory follicle. Ovulation occurs about 28 h after the initiation of the LH surge.

The remainder of this manuscript will provide more depth on this simplified view of the estrous cycle by summarizing some recent information on: regulation of follicular development, regulation of corpus luteum function, and how this information can be applied to understanding mechanisms involved postpartum anestrus and development of follicular cysts.