Effects of long-term ad libitum feeding on plasma lipid components and blood glucose, beta-hydroxybutyrate and insulin concentrations in lean adult sheep.

Abstract

The long-term changes in plasma lipid composition and blood glucose, beta-hydroxybutyrate and insulin concentrations in experimental ad libitum fed adult Suffolk sheep were studied and compared with those of control sheep receiving a maintenance diet. The results were interpreted in relation to changes in food intake, body weight and body composition. Plasma lipid distribution was slightly influenced by the intake level and the fattening state. Compared to the maintenance diet, ad libitum feeding induced a decrease in the concentration of plasma free fatty acids (FFA); when the food intake decreased, this FFA concentration increased gradually. The fatty acid composition of the lipid fractions was subject to variation in the long-term ad libitum fed sheep. Myristic and palmitic acids in FFA, palmitoleic acid in triglycerides and linoleic acid in all the lipid fractions showed decreasing values associated with reduced food intake in the fattening sheep. Stearic and oleic acids in FFA, phospholipids and cholesterol esters increased when body weight and body fat increased and food intake decreased; they showed stable values by the end of the experiment, when food intake and body weight and composition also stabilized. Throughout the test, blood glucose concentration remained unaffected. A stable blood beta-hydroxybutyrate concentration, 2 times the control level, was observed from the 4th to the 10th experimental week in the ad libitum fed sheep (phase 1). From the 14th to the 26th experimental week (phase 2), decreased values were associated with increasing body weight and decreasing food intake. From the 30th week on (phase 3), beta-hydroxybutyrate concentration stabilized at a level 50 p. 100 higher than in the control sheep. During the first 6 weeks of ad libitum feeding, the experimental sheep achieved the same plasma insulin concentration as the control sheep. Thereafter a 30-fold increase was noted. Moreover, fluctuations of between 20 and 1 600 microU/ml were observed in fattening phases 2 and 3. This experiment demonstrated that feeding adult sheep ad libitum induces complex interrelationships between food intake and fattening state on the one hand and several blood substances on the other. Other experiments are needed to clarify these interrelationships.