AbstractIncreased capability for mi

Abstract
Increased capability for milk production has been associated with a decline in fertility of lactating cows. Nutritional requirements increase rapidly with milk production after calving and result in negative energy balance (NEBAL). NEBAL delays the time of first ovulation through inhibition of LH pulse frequency and low levels of blood glucose, insulin and insulin-like growth factor-I (IGF-I) that collectively restrain estrogen production by dominant follicles. Up-regulation of LH pulses and peripheral IGF-I in association with the NEBAL nadir facilitates ovulation. NEBAL reduces serum progesterone concentrations and fertility. Diets high in crude protein support high milk yield, but are also associated with lower reproductive performance. High protein can result in elevated plasma urea concentrations that affect the uterine environment and fertility. Nutritional interactions resulting in poor fertility of high producing dairy cows include the antecedent effects of NEBAL and effects of high dietary protein.

Keywords
Dairy cattle; Nutrition; Reproduction