Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 16, 1998
Publication Date: N/A
Interpretive Summary: Feed requirements for the ewe are their highest while the ewe is nursing. This peak period of nutrient requirement frequently coincides with the period that grazed forage availability is at its lowest. As a result, supplemental feed is required. To increase the efficiency of lamb production, it is important to feed the correct nutrients in the appropriate quantities during nursing to reduce cost. However, little is known about what nutrients are required and how much of each is needed. When the ewe is producing milk, the stomach-intestinal complex and liver are primary users of energy. The rate of energy use by these tissues increases with increased milk production. Increased milk production requires an increase in glucose removal from the blood by the mammary gland. We have identified that glucose release into blood by the liver increases as the level of milk produced increased and the level of the increase is nearly equal to the amount required for increased milk synthesis. We also found that energy use by the liver increases with increased glucose release into the blood. These finding have demonstrated some of the biological mechanisms that contribute to the increase in energy used by the ewe during milk production. Identification of the metabolic requirements of the ewe during the production cycle will allow for the development of feeding systems that meet nutrient needs rather than feeding systems that rely on meeting nutrient requirements based on energy and nitrogen usage.
Technical Abstract: The objectives of this study were, first, to determine the relationship between milk production and hepatic glucose release and, second, to determine the relationship between milk production and net hepatic uptake of gluconeogenic precursors. Nine multiparous ewes were individually penned and fed an alfalfa hay based diet ad libitum. Catheters were surgically placed in the portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta. Metabolite fluxes across the portal-drained viscera and liver were subsequently measured at 1, 3, 6, and 10 weeks after parturition. Net hepatic glucose release (P < 0.001), net hepatic lactate uptake (P = 0.02), and net hepatic propionate uptake (P = 0.047) increased with increased milk production. Hepatic oxygen consumption increased with increased net hepatic glucose release (P < 0.001). Net hepatic glucose release increased with increased hepatic propionate uptake (P = 0.003) and tended to increase with increases in metabolized amino acid (P = 0.12) and lactate uptakes (P = 0.07). The observed increases in oxygen consumption by the portal drained viscera with increased milk production was probably the result of increased nutrient flux. Increased hepatic oxygen consumption with increased milk production was probably due to increased glucose and urea synthesis.