1. a young domestic fowl up to the age at which the bird can survive without supplementary heat and feed. In some poultry industries that is about 4 weeks. However, the endpoint varies with the type of husbandry practiced. In the North American poultry industry a chicken is any domestic fowl up to about 20 weeks of age.
2. any young bird.

• c. anemia — bone marrow hypoplasia with thymic and bursal atrophy in young chicks caused by a circovirus (genus Gyrovirus). The disease is characterized by weakness, pallor and a high mortality rate. Secondary bacterial, viral and fungal infections are commonplace including hemorrhagic syndrome, anemia, dermatitis and blue wing disease.
• c. body louse — menacanthus stramineus.
• c. bronchitis — see avian infectious bronchitis.
• day old c's — newly hatched chicks are delivered in large flat cardboard boxes from the multiplier to the broiler grower—the universal means of shipping live chickens.
• c. edema disease — a disease of broiler chickens fed on a diet containing fat contaminated by one of several toxic factors which cause hepatic necrosis. It is manifested clinically by drooping, dyspnea, death. At necropsy there are large accumulations of fluid in body cavities and a swollen liver and kidneys. The disease is caused by a toxic fat containing dioxin added to the ration of the birds. Called also toxic fat disease.
• c. embryo chondrodystrophy — caused by nutritional deficiency of manganese. Characterized by short, thick legs, short wings, parrot beak, retarded down and body growth.
• c. embryo lethal organ (CELO) virus — see quail bronchitis.
• c.-fat clot — clots that develop after death; largely devoid of red blood cells. More common in animals that have had anemia or in which blood sedimentation was increased. Seen more often in horses than in other species.
• c. fluff louse — goniocotes gallinae.
• c. head louse — see cyclotogaster heterographa.
• c. hemorrhagic syndrome — see inclusion body hepatitis.
• c. louse — see menopon pallidum, menacanthus stramineus.
• c. mite — see dermanyssus gallinae.
• c. pox — see avipoxvirus.
• c. sexing — usually carried out on day-old chickens by examining inside the vent for small eminences. Up to 1000 chickens can be sexed per hour with 98% accuracy.
• sticky c. — sticky, edematous chickens caused by hatching at too low or too high humidities.