Modern broiler chickens have been bred for extraordinary feed conversion efficiency. The welfare costs of this breeding — leg disorders, cardiovascular failure, and chronic discomfort — affect billions of birds.
The welfare cost of modern broiler breeding is systematic and severe. Birds bred for maximum feed conversion efficiency carry bodies that their legs and hearts cannot adequately support. Chronic leg pain from skeletal disorders means many birds spend increasing time lying in litter as they approach slaughter weight, unable to move comfortably to access feed and water. The pain level in lame broilers, assessed through gait scoring and preference testing, is clinically significant. Cardiovascular failure kills millions of birds suddenly — the remainder are chronically compromised physiologically. This is not incidental welfare failure but a predictable consequence of extreme selection for a single production trait at the expense of all others.