Oxygen consumption by and blood flow across the portal-drained viscera and liver of pregnant ewes.

The energy requirement of ewes increases during pregnancy. In late pregnancy, approximately 40% of the increase in heat production can be attributed to increases in heat production by nonreproductive 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 allowed ad libitum access to an alfalfa hay-based diet. 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 lambing. 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 lambing. 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 than in ewes with a single fetus independent of changes in feed intake. Hepatic oxygen consumption increased with duration of gestation and was estimated to account for 40% of the heat production not associated with the gravid uterus.