Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 23, 1997
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 feed cost. 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 nursing. It was found that the rate of energy use by the liver increases with increased milk production. The primary energetic cost at the liver is associated with modification of nutrients that are not available for milk synthesis to nutrients that are available. Identification of the liver's role in providing the required nutrients to support 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.
The objectives of this study were to determine portal-drained viscera and liver oxygen consumption in the lactating ewe and to determine the relationship between milk production and oxygen consumption by these tissues. 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. Oxygen consumption by the portal-drained viscera and liver were subsequently measured at 1, 3, 6, and 10 wk after parturition. The percentages of fat, protein, and solids-not-fat in milk decreased as milk production increased; however, yields of fat, protein, and solids-not-fat increased with increased milk production. Portal-drained visceral and hepatic oxygen consumption increased with increased milk yield. Milk energy yield increased with increased milk yield. These results indicate that the efficiency of milk energy secretion relative to energy expenditure by these tissues increases with increased milk production.