Breast muscle myopathies including woody breast and white striping are welfare problems caused by extreme selection for breast muscle mass in modern broiler chickens, causing chronic muscle disease in fast-growing birds.
Breast myopathies represent welfare harm directly caused by genetic selection decisions prioritizing productivity over health. The rapid muscle growth of modern broiler breeds outpaces the vascular supply needed for adequate oxygenation, causing focal ischemia and muscle fiber necrosis that results in chronic muscle inflammation and pain. Birds with woody breast have persistent muscle disease throughout their short lives — a welfare harm embedded in their genetics. The prevalence of these conditions — affecting the majority of fast-growing birds — means the aggregate welfare impact is enormous: billions of birds annually experience chronic muscle disease as a direct consequence of industry selection decisions. Transitioning to slower-growing breeds, as required by the Better Chicken Commitment, substantially reduces breast myopathy rates and represents one of the most impactful welfare improvements available in chicken production.