Abstract: Beak lesions were observed in 50-weeks-old broiler breeder roosters reared under a separate sex mash diet feeding, with low in protein and energy for roosters. All roosters kept with hens showed deformities in the upper and lower beak but the lesions were not found in roosters kept separately. Hens' feed troughs had been covered with galvanized wire grids
to exclude the males eating from hens' troughs. There was approximately 5% mortality among roosters with the beak lesions. A marked reduction (23%) on hatchability was observed, but no change in egg production occurred. The beak lesions were the major cause of male's culling in the flock.Histopathological examination of the lesions revealed that the epidermis, keratin layer and underlying connective tissue of the beaks were severely
affected by necrosis. Bacteriological cultures yielded, mainly, growth of hemolytic Staphylococcus aureus, and hematological tests showed a mild increase in the number of the white blood cells. The case reported here appeared to be a management-related problem. These findings have implications for poultry industry. J.Vet.Res. 62,2:33-36,2007.