NUTRITIONAL AND HORMONAL INTERRELATIONSHIPS IN BEEF-CATTLE REPRODUCTION

Reproductive rate has a major influence on production efficiency of beef cattle, and nutritional mnagement is the main limiting or controlling factor for reproduction. Decreased availability of energy is the most common problem studied in beef cattle management and will be the primary focus of this review. In order to effectively manage energy nutrition, we need a better understanding of how this variable affects the various phases and control mechanisms of reproduction. Insufficient energy intake because of dietary quality or quantity will delay puberty, lengthen postpartum anestrus and cause anestrus in cows or heifers that are having estrous cycles. Energy intake has effects on a wide variety of endocrine, neural and metabolic mechanisms. Effects include changes in gonadotropic hormone secretion from the pituitary, production of progesterone during both the estrous cycle and pregnancy, differential sensitivity of the pituitary-hypothalamus to steroids and releasing hormones and changes in ovarian activity measured by hormone secretion, follicular development and ovulation. All of these effects of dietary energy have been shown to be variable. This variation in response seems to be related to differences in degree of energy restriction, body condition score and whether body weight is stabilized or changing. Glucose may be the specific energy source through which energy manifests its effects on reproduction.