Influence of protein concentration on the sulphur‐containing amino acid requirement of broiler chickens1

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Abstract
1. Two experiments were conducted with male broiler chickens from 3 to 6 weeks of age to determine the effect of dietary protein content on the requirement for sulphur amino acids (SAA). In experiment 1, 0, 0.5, 1.0 or 1.5 g DL‐methionine/kg were added to diets calculated to contain 200, 240 or 280 g protein/kg. In experiment 2, 0, 0.6, 1.2 or 1.8 g DL‐methionine/kg were added to diets calculated to contain 160, 180 or 200 g protein/kg. 2. In experiment 1, the SAA requirement for body weight gain increased as dietary protein content increased. Regression analysis indicated a requirement of 38 g SAA/kg protein. 3. In experiment 2 in which lysine supplementation provided a minimum of 10 g/kg, the requirement for SAA per unit of diet increased only slightly as protein concentration increased indicating that below 200 g protein/kg of diet, the SAA requirement increases per unit of protein with supplementation of the second‐limiting amino acid. 4. Abdominal fat percentage declined in a linear manner with each increment of SAA added to diets containing 160 to 200 g protein/kg. Adding methionine to diets containing 240 or 280 g protein/kg did not affect abdominal fat content. A lower limit of abdominal fat was achieved with a protein concentration of 240 g/kg. 5. It is concluded that the requirement for SAA of finishing broiler chickens is directly related to protein content at concentrations of 200 or more g protein/kg but increases per unit of protein at lower protein concentrations when a minimum lysine concentration is specified. Abdominal fat content reaches a minimum between 200 and 240 g protein/kg of a maize‐soyabean meal diet regardless of SAA content.