In breeders and layers, the clinical signs of HPAI infection include cyanosis of the head, necrosis of the comb and wattles, torticollis, coughing, and yawning. Diarrhoea is common, often with greenish faeces. Egg production drops, shells become soft, and misshapen eggs appear. Some eggs may have no shell at all. Eggs are pale, and hatchability decreases. Small eggs (approximately 10% of total production) are often observed.

This breeder hen shows respiratory signs and conjunctivitis in a case of an H9N2 outbreak.