Control and management of ovarian follicles in cattle to optimize fertility.

Experiments were designed to elucidate the control of ovarian follicle turnover and the impact of follicular dynamics on the subsequent fertility of dairy cattle. An experimental model was established to examine the interrelationships of gene expression for steroid enzymes, the insulin-like growth factor system and inhibin production as associated with follicle selection, dominance and atresia. Follicular dynamics during the postpartum period and the oestrous cycle are shown to be altered markedly by the metabolic demands of lactation. The feeding of ruminally-inert fat stimulated follicular development and improved reproductive performance. The development of persistent follicles during oestrus synchronization causes a reduction in fertility that can be corrected by recruitment and selection of a new ovulatory follicle after the injection of a gonadotrophin-releasing hormone agonist. Present systems of oestrus synchronization need to consider both synchronization of follicular development and corpus luteal regression in order to optimize fertility. With current systems manipulating follicle development, the potential to implement a timed insemination programme to improve reproductive management exists. Ovulation of the first-wave dominant follicle with human chorionic gonadotrophin provides a means to markedly enhance concentrations of plasma progesterone in the luteal phase.