Endocrine regulation of energy metabolism in ruminants.

Partitioning of nutrients among tissues of the body is one role of the endocrine system. Skeletal muscle, adipose tissue, and lactating mammary gland are tissues that utilize most of the energy consumed in excess of maintenance. The energy metabolism of ruminants is complicated by the lack of absorption of glucose because of the fermentation of carbohydrates in the rumen. Increased secretion of glucagon after feeding promotes hepatic gluconeogenesis from absorbed amino acids. During fasting, gluconeogenesis is maintained by increased secretion of glucocorticoids. Based on observation form a number of diverse experiments with cattle and sheep, it seems that growth hormone increases the flow of energy to skeletal muscle and the mammary gland, whereas insulin increases the utilization of energy by the adipose tissue. Nutritional and genetic factors associated with secretion of these hormones are discussed.