Effects of peptide source on microbial protein synthesis and nitrogen digestion in steers fed high concentrate diets

A. Yusof Hamali

Abstract

Six steers fitted with rumen and duodenal cannulas were used in a replicated 3 x 3 latin square to determine the effects of peptide source on the efficiency of microbial protein synthesis and N digestibility. Steers were fed corn-based diets supplemented with three different sources of nitrogen. The three treatment diets consisted of 1) corn + casein (CC), 2) corn + soybean meal (CSBM), and 3) corn + urea (CU). Mean ruminal NH3-N concentrations for CC, CSBM and CU diets were 7.13, 5.93 and 9.27 mg/dl, respectively. Steers supplemented with SBM had higher ruminal peptide-N concentration (p <0.02) and amino acid-N concentration (p <0.03) than steers supplemented with casein. Mean ruminal concentrations of peptide-N for CC, CSBM and CU diets were 56.67, 66.82 and 1.66 mg/liter respectively. Efficiency of microbial protein synthesis was not altered by ruminal peptide-N concentrations and averaged 13.89 g of microbial N/kg of organic matter (OM) digested for all treatments. Supplementation with SBM and casein tended to increase microbial N and NANMN flow but the difference between them was not significant (p <0.08). Mean microbial N entering duodenum averaged 65.0, 67.2 and 59.0 g/d for treatments CC, CSBM and CU respectively. Steers receiving SBM had 7.1% more microbial N flow to duodenum than steers receiving urea. Faecal N excretion was greater for steers receiving urea or casein than for steers receiving SBM (p <0.02, p <0.04) but total tract N digestibilities were similar among treatments. Efficiency of microbial protein synthesis was not increased by feeding diets that increased the concentration of peptides in the rumen.

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