Influence of Source of Nitrogen on Performance and Plasma Amino Acid Patterns of Lambs

Abstract

Comparisons were made of the value of supplementing semipurified or natural diets with SBM, CGM, urea or various combinations of nitrogen from these sources in five growing-fattening trials with lambs. Blood plasma amino acid levels were determined in lambs fed the semipurified diets. SBM was superior to CGM as a nitrogen source in semipurified diets for promoting lamb growth, but was not superior in natural diets. Urea as the major source of nitrogen in semipurified diets was inferior to SBM or CGM. In natural diets, there was a tendency for performance of lambs fed urea to be inferior to that of those fed SBM or CGM. The incorporation of urea into semipurified diets containing CGM generally resulted in gains equal to those of lambs fed SBM as the major source of nitrogen. Urea supplementation of natural diets containing CGM did not improve growth performance. Lambs fed combinations of SBM and CGM in both semipurified and natural diets performed similarly to lambs receiving SBM alone as the major source of nitrogen. Blood plasma amino acid patterns differed considerably between lambs fed nitrogen from different sources. Plasma concentrations of lysine and leucine appeared to be related to the amino acid levels in the dietary protein. Plasma levels of phenylalanine, glycine, serine, tyrosine and proline also varied with source of dietary nitrogen.