Effects of Dietary Energy Level and Protein Source on Site of Digestion and Duodenal Nitrogen and Amino Acid Flows in Steers

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Abstract
Six steers (468 kg) with ruminal and duodenal cannulas were fed diets formulated for two levels of energy containing three crude protein (CP) sources in a 6 × 6 Latin square with a 2 × 3 factorial arrangement of treatments. Energy levels were 2.17 and 2.71 Meal metabolizable energy (ME)/kg dry matter (DM) provided by hay-corn (H) and corn silage-corn (CS) diets, respectively. Soybean meal (SBM), corn gluten meal-urea (CGM) and urea (U) provided 33% of dietary CP in 12% CP diets. Apparent organic matter (OM) digested in the stomach was not affected (P > .05) by energy level or CP source, but OM truly digested in the stomach was greater (P < .05) when steers were fed the CS compared with the H diet. Duodenal flow of non-NH3 N was greater (P < .05) when steers were fed CS compared with H and when fed SBM or CGM compared with U. Efficiency of bacterial protein synthesis and duodenal bacterial N flow were increased (P < .05) when steers were fed CS, but non-NH3, nonbacterial N flow to the duodenum was increased (P < .05) when steers were fed H. When steers were fed CS rather than H, flows (g/d) of bacterial amino acids were greater (P < .05), but flows of nonbacterial amino acids tended (P < .08) to be less. Total amino acid flows were not affected (P >.05) by energy level. Duodenal flows of total amino acids tended (P < .06) to be greater when steers were fed CGM compared with SBM or U, due mainly to an increased (P < .05) flow of nonessential amino acids. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science