RELATIONSHIP BETWEEN DIETARY PROTEIN CONTENT AND PLASMA AMINO ACIDS IN SHEEP FED PURIFIED DIETS

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Abstract
Semipurified diets, varying in crude protein (CP) content (6, 10, 15, and 22% CP), were each fed to one wether and plasma amino acid (PAA) concentrations were determined at 0, 15, 30, 60, 120, 240, and 360 min postfeeding. Total essential amino acid concentrations for the 6, 10, and 15% CP rations were 47.2, 76.4, and 72.9 μmol/ml, while nonessential amino acids totalled 88.3, 110.0, and 104.9 μmol/ml, respectively. In general, PAA concentrations were depressed by the low protein diet, except for glycine, which was elevated, and threonine and alanine, which were not affected. PAA concentrations gradually decreased with time after feeding. There was no evident relationship between PAA levels and amount of feed consumed at these time intervals. Lysine was probably the most limiting amino acid, based upon PAA concentrations on the low protein diet compared to average PAA levels for all diets. PAA concentrations reflected dietary nitrogen content. The results suggest that PAA levels were not involved in the regulation of voluntary intake when the diet contained sufficient protein to meet the requirements of the animal.