Influence of metabolic hormones and nutrition on ovarian follicle development in cattle: practical implications.

Nutrition has long been known to have a profound influence on reproductive performance of female cattle, but the underlying mechanism remains poorly understood. Whilst early investigations focused on the modulation of nutrition on hypothalamic-pituitary axis, more recent studies have tested the hypothesis that metabolic hormones as nutritional signals exert a direct effect at the ovarian level. In cattle, treatment with recombinant bovine somatotrophin (rGH) significantly increases the population of small ovarian follicles. This is associated with increases in circulating concentrations of insulin and insulin-like growth factor-I (IGF-I). Subsequent studies, both in vitro and in vivo, have highlighted the importance of IGF-I and/or insulin acting in synergy with FSH and LH. More recently, we demonstrated that feeding heifers with 200% maintenance requirements for a short period significantly increases circulating insulin concentrations and population of small ovarian follicles. Based on these findings, our recent work has aimed at addressing some practical problems in cattle production. Firstly, we showed that both rGH pretreatment and increased dietary intake significantly enhance the response to standard superovulatory regimes. Secondly, we have demonstrated that feeding a diet to increase circulating insulin concentrations during the early lactation can advance the first ovulation postpartum and increase conception rate to the first service in dairy cows. In summary, nutrition influences ovarian follicle development in cattle possibly through changes in metabolic hormones. These interactions can be manipulated to improve reproductive performance.