Control of Ovulation Rate in Beef Cattle.

Abstract

Under intensive production systems, the greatest potential for effecting increases in production and economic efficiency in the beef cow herd lies in the possibility of increasing the frequency of twin births. Embryo transfer is technically a successful method of inducing twin births in cattle. While an embryo transfer approach is too costly to allow commercial twinning, it has been used to show that ovulation rate and not uterine capacity is the limiting factor in increasing the reproductive rate of the cow. While ovulation of one or more viable oocytes is central to normal reproduction, knowledge of the control of ovulation and of folliculogenesis on which ovulation depends, is limited. In spite of the fact that many follicles are subjected to the same endogenous hormonal environment and theoretically should all be capable of ovulating, only a tiny proportion do. While gonadotrophic hormones play a central role in ovarian follicle development and ovulation, their action at the ovarian level seems to be controlled by intra-ovarian factors. This intra-ovarian control of ovulation is thought to be exerted partly by the hormone inhibin and partly by other, as yet, unidentified compounds in follicular fluid. This project focused on identification and isolation of ovarian compounds involved in the control of ovulation rate, followed by immunisation against these compounds in order to study the effect on ovulation and the twin calving rates. The main results are summarised here and detailed results have been published in the papers listed at the end of this report.