Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/1999
Publication Date: 5/1/2000
Citation: Freetly, H.C., Ferrell, C.L. 2000. Net flux of nonesterified fatty acids, cholesterol, triacylglycerol, and glycerol across the portal-drained viscera and liver of pregnant ewes. Journal of Animal Science. 78:1380-1388. Interpretive Summary: Feeding during pregnancy has been identified as a principle cost in the production of lamb and beef. Female ruminants require specific nutrients to optimize feed efficiency during pregnancy; however, little is known about the nutrients that are required and how much of each is needed. In this study the effect of pregnancy on the transport of nutrients across the estomach-intestinal complex was measured. Nutrients required for the growt of the fetus are not readily available from the nutrients absorbed from the stomach and intestines of the female. In order to supply the nutrients required for fetal growth, the maternal liver converts metabolites not used in fetal growth to nutrients available for fetal growth. In this study, the role of the liver in the conversion of nutrients during the different stages of pregnancy were measured. This study has identified some of the metabolic events that result in the increase in nutrient requirements of the ewe during pregnancy. During late pregnancy, fatty acids and glycerol are primary substrates for liver metabolism. These data suggest that adequate adipose stores should be available during late pregnancy to support the increase in nutrient demand. The extent to which adipose tissue contributes to hepatic metabolism in the pregnant ewe may further be amplified when nutrient availability is reduced.
Technical Abstract: The objective of this study was to determine the pattern of nutrient flux across the PDV and liver in ewes with varying numbers of fetuses. Plasma flow and net cholesterol, nonesterified fatty acids (NEFA), and glycerol release across the PDV and liver were determined prior to exposure to rams. Ewes were then mated. Additional measurements were taken 103, 82, 61, 39, 19, and 6 d before parturition. There was a net PDV uptake of nonesterified cholesterol in the nonpregnant ewes and a net release in the ewes with singles and twins. There was a net hepatic release of nonesterified cholesterol in ewes with twins and a net hepatic uptake in the ewes with singles and in nonpregnant ewes. There was a net PDV release of NEFA; but it did not differ with litter size or days from parturition. Hepatic NEFA uptake increased with litter size and increased as gestation progressed. There was an interaction between litter size and days from parturition for net PDV glycerol release. Net PDV glycerol release in the nonpregnant ewes decreased over time while release in pregnant ewes tended to increase in time. In general, hepatic glycerol uptake increased with litter size and increased as gestation progressed. There was a net PDV uptake of triacylglycerol but it did not differ with litter size or with days from parturition. There was a net hepatic release of triacylglycerol but it did not differ with litter size or with days from parturition. In the nonpregnant ewe the combined contribution of glycerol and NEFA carbon accounted for 10% of the carbon taken up by the liver and in ewes pregnant with twins 19 d before parturition the combine contribution accounted for 42% of the carbon uptake.