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See R. Moreng and J. Avens, Poultry Science and Production (1985); R. E. Austic and M. C. Nesheim, Poultry Production (13th ed. 1990).
a domestic bird of the order Galliformes. Descended from the wild jungle fowl, chickens are the most widely domesticated species of poultry. They are raised for their meat and eggs, and their feathers and down are also used.
Chickens are classified by their principal products into egg, dual-purpose (meat and eggs), and meat breeds. Each has specific anatomical and physiological characteristics. Laying hens are small, grow rapidly, and mature early. The meat and dual-purpose breeds are larger, have well-developed muscles, and mature later.
Roosters develop bony processes, spurs, on the lower part of the metatarsus. Both hens and roosters have crests, which come in such shapes as leaf (with several teeth), rose, and pea. Hens of egg breeds most commonly have leaf crests, which fall to the side at the second or third tooth. The beak is slightly curved. In most breeds, the beak and metatarsus are the same color: yellow, pale pink, black, and so on. Plumage color varies.
Hens of egg breeds weigh 1.8–2.2 kg and roosters, 2.7–3.0 kg; of dual-purpose breeds, 2.5–3.0 kg and 3.5–4.0 kg; and of meat breeds, 3.0–3.5 kg and 3.5–4.5 kg. Chicks at birth weigh 30–35 g. Chicks of dual-purpose breeds at 70–80 days usually weigh 20–30 percent more than those of egg breeds. Broilers attain a weight of 1.5–1.6 kg by 60–65 days of age. The white meat of broilers is a dietetic product; it contains over 20 percent complete proteins and only 5–7 percent fat.
Hens reach sexual maturity (age at the time of laying the first egg) at five or six months. Birds of egg breeds mature earlier than those of dual-purpose breeds. Annual production of layers is 200–220 eggs and at the best purebred farms, 220–250 (the record is 365). The highest egg production is found in crossbred and interlineal hybrid birds selected for egg productivity and egg quality. A hen’s early eggs weigh 40–50 g; by the age of one year she lays eggs weighing 55–65 g. Hens of dual-purpose breeds lay smaller eggs than those of laying breeds. Egg laying ceases in hens with the onset of molting, which in good layers lasts for two to three weeks and two months or more in poor ones. After molting, hens resume laying if feeding and maintenance conditions are good.
Hens are capable of laying eggs for approximately ten years. Commercial farms use hens only during the first year of egg laying for economic reasons: egg production decreases with age by 10–15 percent each year. On purebred farms they are used for two to three years, and only highly productive birds are kept for the second and third years. A purebred flock usually consists of 55–60 percent pullets, 30–35 percent two-year-olds, and 10 percent three-year-olds. Roosters are used up to two years (the more valuable ones three years). The sex ratio in a purebred flock is one rooster for eight to 12 hens.
Hens may be kept without roosters when only food eggs are desired. The instinct for brooding is poorly developed in the majority of cultivated breeds, and eggs are hatched in incubators. The period of embryonic development of a chick averages 21 days. Incubation of all eggs suitable for hatching will yield several dozen chicks from each hen.
Chickens are kept in poultry houses (on the floor or in cages). Rations include grain of two or three types—for example, corn and barley (65–70 percent of the weight of all dry fodders), oilcakes and grist (8–12 percent), and dry animal fodders—fish meal and meat-and-bone meal (3–5 percent), dried yeast (1–3 percent), edible roots and tubers, grass meal, mineral fodders, and vitamin supplements. In countries where poultry raising is well developed, the commercial feed industry manufactures ready-mixed formulas for all ages of chickens. Large specialized chicken and egg farms produce eggs and poultry meat on a commercial basis. The principal tasks of chicken breeding are developing specialized egg-laying and meat lines and testing them for matching and crossbreeding to obtain hybrid layers and broilers.
REFERENCESFauna SSSR: Ptitsy, vol. 1, issue 4. Moscow-Leningrad, 1941.
Sel’skokhoziaistvennaia ptitsa. Edited by E. E. Penionzhkevich, vols. 1–2. Moscow, 1962.
Smetnev, S. I. Ptitsevodstvo, 5th ed. Moscow, 1970.