Effects of diet with an improved amino acid balance on crossbred steers’ fattening performance and urinary nitrogen excretion

Abstract

The effects of feeding a diet with an improved amino acid balance on weight gain, carcass traits, the fatty acid composition of ribeye, and urinary nitrogen excretion in crossbred steers (Japanese Black and Holstein) were investigated. In study 1, a middle-to-late fattening trial, 12 steers (control group) were fed a conventional diet, and 12 steers (experimental group) were fed a diet that had a reduced protein content and was supplemented with rumen-protected lysine and rumen-protected methionine. The average daily weight gain was 1.14 kg/day in the control group and 1.20 kg/day in the experimental group, a nonsignificant difference being observed. There were no significant effects of the experimental diet on the carcass weight, ribeye area, rib thickness, subcutaneous fat thickness, BMS, BCS, BFS, or crude fat content or fatty acid composition of ribeye. In study 2, the same two diets were tested in four steers at the middle fattening stage in a 2×2 crossover design. The urinary nitrogen excretion in the experimental group was significantly decreased versus the control group (P<0.05). These results indicate that feeding crossbred steers a diet with an improved amino acid balance during the middle- and later-fattening stages can reduce nitrogen excretion without suppressing productivity.