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” (hemor-rhagic 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 ≤ 0.01). This result was due to the higher incidence of carcasses affected by both early (0.94 vs. 0.26%; P ≤ 0.01) and old (0.33 vs. 0.09%; P ≤ 0.01) developing stages of DPM in Ross 508 birds.