Submitted to: Energy Metabolism of Farm Animals Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 27, 1997
Publication Date: N/A
Interpretive Summary: Feed requirements are at their highest when ruminants are pregnant and while they are producing milk. Feed required during this period has been identified as a principle cost in the production of lamb and beef. Specific nutrients are required to optimize feed efficiency during pregnancy; however, little is known about what nutrients are required and how much of each is needed. In this study we have identified the stomach intestines, and liver as primary users of energy during pregnancy and lactation. The rate of energy use by these tissues increases as pregnancy progresses, and remains high while the female is producing milk. Energy expenditure at the liver is primarily associated with modification of nutrients that are not usable for fetal growth and milk production to nutrients that are usable. This study demonstrated that the liver releases the amount of glucose required to support growth of the fetus and milk production. Identifying the liver's role in providing the required nutrients to support fetal growth and milk production will allow for the development of feeding systems that more efficiently provide those nutrients, thereby reducing the energetic cost and increasing the efficiency of feed utilization.
Technical Abstract: Limited information is available on the relative contribution of different maternal tissues to the increase in heat production during pregnancy and lactation. The objectives of this study were to determine, the pattern of net glucose release and oxygen consumption by the PDV and liver during gestation and lactation. Seven multiparous ewes had catheters surgically placed in the portal vein, a branch of the hepatic vein, a mesenteric vein and the abdominal aorta. Ewes were bred 54 d following surgery. Blood flow and net nutrient flux across the PDV and liver were determined at -154, -105, -84, -63, -42, -21, -7, 7, 21, 42, and 70 (SD=+/-3) d from parturition. Portal venous blood flow was decreased in midpregnancy (-84 through -42 d). Portal venous blood flow in late pregnancy and during lactation did not differ from nonpregnant blood flow rates (P > .05). Hepatic venous blood flow at -21, 7, and 21 d from parturition was higher than when animals were not pregnant (P < .05). With the exception of d -7 hepatic arterial blood flow in late pregnancy through mid lactation (-21 through 42 d) was higher than early- through mid-pregnancy (P < .05). Both hepatic and PDV oxygen consumption increased as the pregnancy progressed. Hepatic and PDV oxygen consumption remained high through early lactation before decreasing in late lactation. Net hepatic glucose release followed a pattern similar to that of hepatic oxygen consumption. With the exception of -21 and 42 d, net PDV glucose release did not differ from zero. These data support the hypothesis that part of the increase in energy required during pregnancy and lactation is due to an increase in hepatic energy metabolism. These data suggest that hepatic glucose production is regulated to meet the glucose requirements of the body.