Estimation of the Extent of Conversion of Dietary Zein to Microbial Protein in the Rumen of Lambs

Abstract

A metabolism experiment was conducted to estimate the extent of conversion of dietary nitrogen to microbial protein in the rumen of lambs fed purified diets. Zein was fed as the nitrogen source with 2 cellulose-to-starch ratios. Physical fractionation procedures showed 26.3 and 30.5% microbial protein in the abomasal fluid of lambs fed the high cellulose and high starch diets, respectively. Based on the changes of lysine ratios between the diet and abomasal fluid, the percentage microbial protein was estimated to be 28.0 and 23.8 with the high cellulose and high starch diets, respectively. Using the estimates of conversion based on physical separation of abomasal fluid protein, and using the amino acid compositions of zein and microbial protein, a predicted amino acid composition of abomasal fluid with the 2 diets was calculated. Predicted values were similar to determined values, indicating that amino acid analyses of abomasal fluid might be used to estimate conversion when homologous proteins are fed to ruminants.