The occurrence of deep pectoral myopathy in roaster chickens

A study was conducted to determine the incidence of deep pectoral myopathy (DPM) in male roaster chickens reared under intensive conditions, processed at different ages (from 47 to 65 d of age), and belonging to 2 commercial genotypes (Ross 508 and Cobb 500). The study was carried out in a major Italian processing plant on a total of 120,700 male roaster chickens chosen at random from 151 flocks during a 6-mo period. The evaluation of DPM was performed on pectoralis minor muscles and consisted of a visual assessment of the presence or absence of the myopathy as well as the scoring of muscle damage level as being in an "early" (hemorrhagic appearance) or "old" (gray or green discoloration) developing stage. The average incidence of carcasses affected by DPM was found to be 0.84% (0.62 and 0.22% in early and old stages, respectively). The range in the incidence of total DPM was fairly large and varied from 0 to 16.7%. Considerable variations were also observed for early (range: 0 to 12.0%) and old (range: 0 to 5.6%) developing stages. Considering the effect of genotype, Ross 508 exhibited a higher incidence of DPM in respect to Cobb 500 (1.27 vs. 0.35%; P < or = 0.01). This result was due to the higher incidence of carcasses affected by both early (0.94 vs. 0.26%; P < or = 0.01) and old (0.33 vs. 0.09%; P < or = 0.01) developing stages of DPM in Ross 508 birds.