Changes in body composition in broilers by a sulfur amino acid deficiency during growth.

In the factorial approach, amino acid (AA) requirements are determined using the AA composition of retained protein, which is assumed to be constant. However, this hypothesis may not be valid because the AA composition of body protein can be affected by the diet. The objective of this study was to quantify the changes in chemical body composition of broilers receiving diets either deficient (TSAA-) or sufficient (TSAA+) in TSAA. Diet TSAA+ was formulated according to the Ross recommendation. Diet TSAA- provided 36% true digestible Met:Lys and 64% true digestible TSAA:Lys, which were, respectively, 34 and 22% lower compared with diet TSAA+. Performance and tissue weight gain between 7 and 42 d of age were not affected by the TSAA supply. In TSAA- chickens, protein gain was lower in the carcass (P < 0.01) and tended to be lower in the empty body (P = 0.06) and pectoralis major muscle (P = 0.10). Compared with TSAA+ chickens, lipid gain in TSAA- chickens was 78% greater in the pectoralis muscle (P < 0.001), 28% greater in abdominal fat (P < 0.05), and 10% greater in the carcass (P = 0.10). In the pectoralis muscle, there was a tendency for an increase in the redness value (a*; P = 0.10). The TSAA supply affected the AA composition of tissues and tissue gain, but the Met and Cys concentrations were changed only in the offal (P = 0.08). The deficient TSAA supply resulted in an increase in the Ser concentration in the empty body, carcass, and pectoralis muscle (P < 0.05). In contrast, it resulted in a decrease in the concentrations of Lys and Glu in the empty body, of Phe, Tyr, Gly, and Glu in the pectoralis muscle, and of Ala in the offal (P < 0.05). This indicates that although chickens cope with a TSAA deficiency predominantly by changing the protein and lipid concentration in the body, the AA composition is also affected. This calls into question the use of a constant ideal AA profile in poultry nutrition.