ROLE OF GROWTH-HORMONE AND INTRAFOLLICULAR PEPTIDES IN FOLLICLE DEVELOPMENT IN CATTLE

Ovarian function in cattle is controlled by complex local and systemic feedback mechanisms which ensure that in >96% of estrous cycles only one follicle will ovulate. Although there is a primary requirement for gonadotropins in stimulating follicular growth, particularly during the final stages of follicle maturation, it is now becoming apparent that locally-produced factors, such as insulin-like growth factor-I (IGF-I) and inhibin, have a modulating role. In addition to gonadotropins, other systemic agents such as metabolic hormones (GH, IGF-I and insulin), can also influence follicular growth. The ability to control the growth of the dominant follicle, together with improved understanding of the competing mechanisms controlling follicular recruitment and growth, should enable more precise control of ovarian function and superovulation in cattle.