A METHOD FOR ASSESSING THE NUTRITIONAL STATUS OF GESTATING EWES

The purpose of this study was to identify metabolic changes that occur at low feed intake in order to develop a method to predict the nutritional status of gestating ewes carrying single or multiple fetuses. At about the 5th week of gestation, 32 ewes were assigned equally into treatments of free choice and restricted intakes of chopped orchardgrass hay. The initial intake of each restricted ewe was determined by calculating ration amounts to supply 60% of the NRC crude protein allowance. Feed intake of each ewe was increased weekly to 80 and then to 100% of NRC crude protein allowance according to changes in the metabolites studied. Plasma citrate and nonesterified fatty acids were increased during gestation, but 3-hydroxybutyrate showed the greatest potential for indicating nutritional status of the gestating ewe. Urinary ketones appeared during the 15th week of gestation and in about one-half of the ewes on restricted intake by the 17th week of gestation. At this point, plasma 3-hydroxybutyrate was 0.53 μmol/mL and might indicate a value at which intake adjustment is needed. Total serum protein and blood urea nitrogen (BUN) were decreased by the 20th week of gestation by the ewes fed restricted intakes indicating an effect of restricted feeding on protein metabolism. Increases in both plasma β-hydroxybutyrate and urine ketone bodies by restricted feeding indicated that energy was an early limiting nutrient and that these metabolites may be useful as indicators of nutritional status. Key words: Gestating ewes, predicting nutritional requirements, citrate, nonesterified fatty acids, 3-hydroxybutyrate