Abstract
Two meat-type broiler strains, strain A and strain B, were reared in floor pens (25 birds/pen; 45 pens/strain) for pectoralis (P) major collagen and mixed muscle protein turnover (PT) study from 0-56 D using primary breeder nutrition and husbandry guidelines. Forty broilers (n = 10/strain for collagen PT; n = 10/strain for mixed muscle PT) were selected at each sampling age at day 21, 28, 35, 42, and 56 and infused with 1-13C proline (Pro) and 15N-phenylalanine (Phe) which are used as amino acid tracers for collagen and mixed muscle PT measurements, respectively. Muscle and plasma samples were collected, and enrichments of 1-13C Pro and 15N-Phe were determined using mass spectrometry. Fractional synthesis rate (FSR) and fractional degradation rate (FDR) were measured for collagen and mixed muscle using precursor-product principle. At day 42, after separating the sampled broilers as myopathy (woody breast [WB] score > 1) and nonmyopathy (WB = 0), plasma metabolites were screened for differential 3-methyhistidine (3-MH) expression for both strains. Data were analyzed using one-way ANOVA using t test. Results showed that collagen and mixed muscle FSR and FDR in pectoralis major decreased (P < 0.05) for both strains as the broilers aged. FSR for collagen and FDR for mixed muscle were higher for strain B than those for strain A (P < 0.05). Total collagen was higher (P < 0.05) for strain B. Differentially expressed 3-MH in plasma was higher (P < 0.05) for myopathy-affected broilers indicating greater muscle degradation occurring in myopathy-affected broiler types for both strains. 3-MH Expression in plasma was higher for strain B than for strain A. The research findings showing an increased collagen content per unit muscle weight in pectoralis major in strain B (than in strain A) could be due to higher mixed muscle FDR and increased collagen FSR occurring during the grow-out period. The increased degradation of muscle fibers and probable replacement of muscle-specific protein with connective tissue, mainly collagen, was an evident pathophysiological phenomenon occurring in myopathy-affected broilers.