Outbreak of comb necrosis in layer breeder chickens.

Comb necrosis with leg weakness was seen in 41-day-old female layer breeder chickens. This disease occurred in three flocks at a breeder farm, but not in other flocks of growing chickens and broiler breeder hens at the same farm. The disease started in 35-day-old chicks in three flocks. The morbidity of comb necrosis was 10% and that of leg weakness was 3%. Characteristic gross lesions of affected chickens were swelling and necrosis of the whole comb. Histologically, liquefactive necrosis of epidermal epithelial cells with hyperplasia, vesicle formation in the epidermis, congestion, and hemorrhages with fibrinous thrombi of underlying dermis in the comb were noted. In mature comb lesions, the epidermis showed eosinophilic necrosis (scab formation). In the livers, multiple fibrinous thrombi were present in the sinusoids and there was necrosis of hepatic cells. Staphylococcus aureus and Pasturella spp. were isolated from comb lesions. There were no significant lesions causing leg weakness.