Modern fast-growing broiler breeds reach market weight in 35 days but suffer high rates of leg disorders and cardiovascular problems. Slower-growing breeds offer dramatically better welfare.
The selective breeding of broiler chickens for extreme growth rate is one of the clearest examples of production system design that compromises animal welfare for commercial efficiency. Broiler breeds that reach slaughter weight in five weeks carry leg and cardiovascular systems unable to support their own body weight — they spend increasing proportions of their day lying down, and lying contact with litter causes progressive foot and hock burns. The experience of chronic lameness in the final weeks of life represents significant suffering for millions of birds. Slower-growing breeds, given adequate space and enrichment, show active foraging, play behavior, and dramatically lower rates of leg disorders and cardiovascular disease. The welfare improvement from breed transition is one of the single most impactful changes available to the broiler industry.