The sequence of pathological events in deep pectoral myopathy of broilers

The morphological changes in deep pectoral myopathy of broilers have been studied by light- and electron-microscopy and histochemistry from 15 min to 15 months after its experimental induction. Oedema, mild alterations in some organelles and loss of glycogen were present throughout the supracoracoid muscle within 15 min but its anterior region quickly returned to normal. After 1 hour there were ultrastructural indications of the onset of permanent damage to the muscle and its associated vasculature and by 24 hours there was histological and ultrastructural evidence of ischaemic necrosis and glucan phosphorylase and myosin adenosine triphosphatase were reduced. By 3 days phagocytosis was established at the edge of the ischaemic, necrotic muscle and by 9 days there was capsule formation and active muscle regeneration in this location. Grossly the muscle now had the green periphery and pink interior characteristic of the naturally-occurring myopathy and it subsequently became of drier consistency. At the 3rd week atrophic muscle fibres were seen in the caudal region and by the 6th week this part had become an attenuated band of fibro-adipose tissue containing sparse groups of atrophic muscle fibres. There were morphological indications of reduced numbers of nerve fibres in this region. By the 6th month the atrophic region was unchanged and phagocytosis and overall regeneration had become quiescent. Thus, although regeneration was initially active, the extensive destruction in experimental myopathy was never completely replaced by new muscle.