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 fert ility of dairy cattle. An experimental model was established to examin e the interrelationships of gene expression for steroid enzymes, the i nsulin-like growth factor system and inhibin production as associated with follicle selection, dominance and atresia, Follicular dynamics du ring the postpartum period and the oestrous cycle are shown to be alte red markedly by the metabolic demands of lactation. The feeding of rum inally-inert fat stimulated follicular development and improved reprod uctive performance. The development of persistent follicles during oes trus synchronization causes a reduction in fertility that can be corre cted by recruitment and selection of a new ovulatory follicle after th e injection of a gonadotrophin-releasing hormone agonist. Present syst ems of oestrus synchronization need to consider both synchronization o f follicular development and corpus luteal regression in order to opti mize 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 marked ly enhance concentrations of plasma progesterone in the luteal phase.