Chicken Types, Characteristics & Uses

The market for chicken meat has grown dramatically since then, with worldwide exports reaching nearly 12.5 million metric tons (about 13.8 million tons) by the early 21st century. By the mid-20th century, however, meat production had outstripped egg production as a specialized industry. For most of that period, chickens were a common part of the livestock complement of farms and khelovipbangladesh.com ranches throughout Eurasia and Africa. Each flock of chickens develops a social hierarchy that determines access to food, nesting sites, mates, and other resources. In 2006, scientists researching the ancestry of birds switched on a chicken recessive gene, talpid2, and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils. This stimulates the hen to lose her feathers but also re-invigorates egg-production.

Africa

Chickens are social, inquisitive, intelligent birds, and many people find their behaviour entertaining. Keeping chickens as pets became increasingly popular in the 2000s among urban and suburban residents. Advocates of intensive farming say that their efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in a controlled environment.

• The life span of a chicken varies between 5 – 7 years although there have been cases of chickens living 20 years or so.
• Hens of some breeds can produce over 300 eggs per year; the highest authenticated rate of egg-laying is 371 eggs in 364 days.
• Inbreeding of White Leghorn chickens tends to cause inbreeding depression expressed as reduced egg number and delayed sexual maturity.
• Despite the chicken’s close relationship with the red jungle fowl, there is evidence that the gray jungle fowl (G. sonneratii) of southern India and other jungle fowl species, also members of Gallus, may have contributed to the bird’s ancestry.
• The domestic chicken has subsequently hybridised with grey junglefowl, Sri Lankan junglefowl and green junglefowl; a gene for yellow skin, for instance, was incorporated into domestic birds from the grey junglefowl (G. sonneratii).

Chicken Life Span

In some other countries, flocks are sometimes force-moulted rather than being slaughtered to re-invigorate egg-laying. After 12 months of laying, the commercial hen's egg-laying ability declines to the point where the flock is commercially unviable. According to the Worldwatch Institute, 74% of the world's poultry meat and 68% of eggs are produced this way. The parasite Dermanyssus gallinae feeds on blood, causing irritation and reducing egg production, and acts as a vector for bacterial diseases such as salmonellosis and spirochaetosis.Viral diseases include avian influenza.

Certain breeds, such as silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities. This involves complete withdrawal of food (and sometimes water) for 7–14 days or sufficiently long to cause a body weight loss of 25 to 35%, or up to 28 days under experimental conditions. Hens, particularly from battery cage systems, are sometimes infirm or have lost a significant amount of their feathers, and their life expectancy has been reduced from around seven years to less than two years. Broiler breeds typically take less than six weeks to reach slaughter size, some weeks longer for free-range and organic broilers. Opponents of intensive farming argue that it harms the environment, creates human health risks and is inhumane towards sentient animals. Breeding increased under the Roman Empire and reduced in the Middle Ages.

These chickens may have been introduced during pre-Columbian times to South America via Polynesian seafarers, but this is disputed. The chicks imprint on the hen and subsequently follow her continually. Eggs of chickens from the high-altitude region of Tibet have special physiological adaptations that result in a higher hatching rate in low oxygen environments.

Chickens are gregarious birds and live together as a flock. Chickens will sometimes attempt flight simply to explore their surroundings, however, they will especially fly in an attempt to flee when they perceive danger or pursued by a predator. Hens lay eggs that range in color from white to pale brown and other pale colors depending on the breed. The rooster is larger and more brightly colored than the hen, he also has a larger comb on top of his head. Roosters can usually be differentiated from hens by their striking plumage, marked by long flowing tails and bright pointed feathers on their necks.

In domesticating the chicken, humans took advantage of the red junglefowl's ability to reproduce prolifically when exposed to a surge in its food supply. The chicken (Gallus gallus domesticus) is a domesticated form of the red junglefowl (Gallus gallus), originally native to Southeast Asia. Females (mature hens and younger chickens, called pullets) are raised for meat and for their edible eggs. The chicken is perhaps the most widely domesticated fowl, raised worldwide for its meat and eggs. These domesticated chickens spread across Southeast and South Asia where they interbred with local wild species of junglefowl, forming genetically and geographically distinct groups.

＼ 最新情報をチェック ／