Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 1997
Publication Date: N/A
Interpretive Summary: Feed during pregnancy has been identified as a principal cost in the production of lamb and beef. The female ruminant requires specific nutrients to optimize feed efficiency during pregnancy; however, little is known about what nutrients are required and how much of each is needed. In these studies, the stomach intestinal complex and liver have been identified as primary users of energy during pregnancy. The rate of energy use by the liver increases as the pregnancy progresses. The primary energetic cost at the liver is associated with modification of nutrients that are not available for fetal growth to nutrients that are available. Identifying the liver's role in providing the required nutrients to support fetal growth 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.
The energy requirement of the ewe increases during pregnancy. In late pregnancy approximately 40% of the increase in heat production can be attributed to increases in heat production by non-reproductive tissues. The objective of this study was to determine the pattern of oxygen consumption by the portal-drained viscera (PDV) and liver during pregnancy to allow for an estimation of the extent to which these tissues contribute to the increase in energy requirement. Nineteen 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. Oxygen consumption by the PDV and liver were subsequently measured before breeding and at 6, 19, 39, 61, 82, and 103 d before birth. Hepatic arterial blood flow was not influenced by litter size (P =.89) or stage of pregnancy (P = .28). Portal and hepatic venous blood flow peaked 19 d before birth. Oxygen consumption by the PDV and liver increased with increased ad libitum feed intake. The increase in hepatic oxygen consumption occurred approximately 63 d earlier in ewes with twins compared to ewes with a single fetus independent of changes in feed intake.