Pathology of deep pectoral myopathy of broilers.

Deep pectoral myopathy occurred in 39 of 204 apparently healthy and 46 of 146 ill, adult broiler breeders from Poultry Research Centre flocks. Both sexes and two commercial strains were similarly affected. The myopathy was not associated with any disease except pododermatitis. The supracoracoid was the only muscle affected. It was bilaterally involved in 33 chickens. The lesions were grouped macroscopically into three categories: acute oedema progressing to a green necrosis, centrally located cicatrix, and replacement of the caudal region by fibroadipose tissue. Microscopcially the green lesion consisted of necrotic, anucleate muscle fibres devoid of inflammatory cells and surrounded by a fibrous capsule that had a reactive inner border and externally abutted on normal and regenerating muscle or fibro-adipose tissue. Considered with the ultrastructural findings of early loss of glycogen and disintegration of sarcoplasmic reticulum, mitochondria, nuclei and Z lines, these findings indicate that the condition is an ischaemic necrosis. There was no evidence that its primary cause was occlusive vascular lesions. The muscle was able to regenerate unless extensive secondary neurological lesions were present.