A deficient supply of methionine changes the composition and metabolism of the pectoralis major muscle in growing broilers

Although dietary sulphur amino acids (AA) have been extensively studied, little is known about how differential supplies and sources can affect muscle composition. The aim of this study was to investigate the growth performance, meat quality, composition and protein metabolism of the pectoralis major muscle (PM) in broilers receiving a diet either deficient or sufficient in sulphur AA and either supplemented with DL-Met or DL-2-hydroxy-4-methylthiobutyric acid (HMTBA) during a 3-wk period. For both Met sources, the supply of Met and sulphur AA in the deficient diets was respectively 43% and 30% below those of the sufficient diets. The deficient Met supply reduced the bird final BW, ADG and G:F (P < 0.05). In Met-deficient birds, the relative weight and protein content of PM were lower, and the meat colour was more red and green, whereas the water content was higher (P < 0.01). The absolute protein synthesis and protein mass of PM were lower in Met-deficient birds (P < 0.05) whereas proteasome activity of PM was conversely greater (P < 0.01). In these birds, the His and OH-Pro contents of retained protein in PM were higher (P < 0.01), whereas the Lys, Ile, and Leu contents tended to be lower (P < 0.10), with no change in the Met and Cys contents. Free contents of β-Ala, anserine and balenine of PM were lower in Met-deficient birds, but free contents of His, carnosine, and taurine were higher (P < 0.01). In conclusion, the AA and protein contents of the muscle together with bird growth are changed by a Met deficiency with a potential impact on protein degradation and meat quality. There are no differences between dietary Met (DL-Met) and hydroxy-Met (HMTBA) sources on muscle growth and protein metabolism.