The welfare implications of breast muscle myopathy in modern broiler breeds and the industry response.
Broiler breast muscle myopathy conditions are welfare indicators that reveal fundamental problems with the growth rates achieved in commercial breeds. The degeneration, fibrosis, and abnormal metabolism underlying woody breast and related conditions suggest that breast muscle tissue is growing faster than the circulatory and metabolic systems can support — a form of tissue-level welfare compromise experienced by the majority of commercial broilers. While the subjective suffering caused by myopathy is difficult to assess directly, the conditions indicate that the birds are living at physiological limits that compromise normal tissue function. The correlation between fast growth rates and myopathy, and the near-absence of the conditions in slower-growing breeds, provides clear evidence that the welfare solution is transition to slower-growing breeds — the same intervention that addresses leg weakness, cardiovascular disease, and other welfare problems associated with extreme growth rates.