Relationship between the consumption of oxygen by portal-drained viscera and liver and milk production in the ewe.

The objectives of this study were to determine oxygen consumption by portal-drained viscera and liver in lactating ewes and to determine the relationship between this consumption and milk production. Nine multiparous ewes were individually penned and fed for ad libitum intake a diet based on alfalfa hay. Catheters were surgically placed in the portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta. Oxygen consumption by portal-drained viscera and liver was subsequently measured at 1, 3, 6, and 10 wk after parturition. The percentages of fat, protein, and SNF in milk decreased as milk production increased; however, yields of fat, protein, and SNF increased as milk production increased. Increased oxygen consumption by portal-drained viscera and liver was positively correlated with increased milk energy yield. These results indicated that the efficiency of milk energy secretion relative to energy expenditure by these tissues increases as milk production increases.