Natural mating in broiler parent flocks causes significant welfare harm to broiler breeder hens through forced copulation and injury from oversized males bred for excessive body weight.
The extreme size dimorphism in broiler parent flocks creates a natural mating system where females are physically injured by oversized males pursuing them at high frequency. Feather loss on the backs and heads of hens from male treading is common and causes skin lacerations that become infected. Hens attempting to avoid males show chronic flight behavior that elevates stress levels. This welfare problem is entirely driven by the selection for rapid growth that makes broiler males physically incompatible with natural mating at normal body proportions.