Breast muscle myopathies in fast-growing broiler chickens are a direct consequence of selection for extreme growth rates and represent an inherent welfare problem in conventional broiler genetics.
Breast myopathies are a welfare consequence embedded in the genetics of fast-growing broiler production. Muscles growing faster than the vascular system can supply with oxygen undergo ischemic damage — the same process that causes tissue death in human ischemic events — resulting in fibrosis and fat deposition. This is not an occasional complication but a predictable outcome of selecting for extreme growth rates: the faster the growth, the higher the myopathy prevalence. Affected birds carry degenerating muscle tissue throughout the grow-out period, with the reasonable inference that this causes chronic discomfort. The solution is genetic: slower-growing breeds that do not outpace their vascular supply have dramatically lower myopathy prevalence. The Better Chicken Commitment requirement for slower-growing genetics directly addresses this welfare problem alongside the lameness and cardiovascular conditions it also causes.