Effect of Various Energy Sources upon Plasma Free Amino Acids in Sheep

Abstract

Intra-arterial infusion of energy sources were made in view of the possibility that energy might induce short-term changes in the plasma free amino acid (PFAA) concentration which would in turn reflect the limiting amino acid in ruminants. Changes in the PFAA concentrations after energy infusions are expressed as plasma amino acid indexes (PAAI) and are defined as the (PFAA concentration after energy infusion divided by the PFAA concentration pre-energy infusion) × 100. In the first of three 4 × 4 Latin-square design experiments intra-arterial infusion of glucose depressed the PFAA below the PFAA concentration after saline (control) infusions at both 24 and 6 hours post-feeding. Furthermore, depressions in the essential amino acids after glucose infusions were greater than the decreases in the nonessential amino acids at both times. In the second experiment isocaloric infusions of glucose, propionate, acetate and butyrate resulted in average plasma essential amino acid indices of 59, 66, 90 and 85, respectively. In the last experiment the energy infusions were glucose, acetate, half glucose plus half acetate isocaloric with the first treatments and half glucose plus half acetate at twice the caloric level of the other treatments. All infusions in experiments 2 and 3 were at 24 hours post-feeding. Correlations of the essential amino acid reduction patterns observed after infusion of glucose 24 hours post-feeding with the relative essential amino acid composition of lamb for the 3 experiments were 0.89, 0.72 and 0.94, respectively. The plasma amino acid indexes indicated isoleucine as the limiting amino acid (lowest index) after the following infusions: glucose 24 hours post-feeding (all experiments), propionate, and both half glucose-half acetate treatments in experiment 3.