Chicken

2008/9 Schools Wikipedia Selection. Related subjects: Food

Chicken
A cock (left) and hen (right) roosting together
Conservation status
Domesticated
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Aves Order: Galliformes Family: Phasianidae Genus: Gallus Species: G. gallus
Binomial name
Gallus gallus (Linnaeus, 1758)
Synonyms
Gallus gallus domesticus

The chicken (Gallus gallus, sometimes G. gallus domesticus) is a domesticated fowl likely descended from the wild Indian and southeast Asian Red Junglefowl (Gallus gallus) and the related Grey Junglefowl (G. sonneratii). Traditionally it has been widely accepted that the chicken was descended solely from the former, as hybrids of both wild types tended toward sterility; but recent genetic work has revealed that the genotype for yellow skin present in the domestic fowl is not present in what is otherwise its closest kin, the Red Junglefowl. It is deemed most likely, then, that the yellow skin trait in domestic birds originated in the Grey Junglefowl.

The chicken is one of the most common and widespread domestic animals. With a population of more than 24 billion in 2003, there are more chickens in the world than any other bird. Humans keep chickens primarily as a source of food, with both their meat and their eggs consumed.

Etymology

In the U.S.A., Canada and Australia, adult male chickens are known as roosters; in the UK they are known as cocks. Males under a year old are cockerels. Castrated roosters are called capons (though both surgical and chemical castration are now illegal in some parts of the world). Females over a year old are known as hens, and younger females are pullets. In Australia and New Zealand (also sometimes in Britain), there is a useful generic term chook (rhymes with "book") to describe all ages and both genders.. Babies are called chicks, and the meat is called chicken.

"Chicken" was originally the word only for chicks, and the species as a whole was then called domestic fowl, or just fowl. This use of "chicken" survives in the phrase "Hen and Chickens," sometimes used as a UK pub or theatre name, and to name groups of one large and many small rocks or islands in the sea (see for example Hen and Chicken Islands).

General biology and habitat

Chickens in nature may live for five to eleven years depending on the breed. In commercial intensive farming, a meat Chicken generally lives only six weeks before slaughter. A free range or organic meat chicken will usually be slaughtered at about 14 weeks. Hens of special laying breeds may produce as many as 300 eggs a year. After 12 months, the hen's egg-laying ability starts to decline, and commercial laying hens are then slaughtered and used in baby foods, pet foods, pies and other processed foods. The world's oldest chicken, according to the Guinness Book of World Records, died of heart failure when she was 16 years.

Roosters can usually be differentiated from hens by their striking plumage, marked by long flowing tails and shiny, pointed feathers on their necks and backs (the hackles and saddle)—these are often colored differently from the hackles and saddles of females.

However, in some breeds, such as the Sebright, the cock has only slightly pointed neck feathers, the same colour as the hen's. The identification must be made by looking at the comb, or eventually from the development of spurs on the male's legs (in a few breeds and in certain hybrids the male and female chicks may be differentiated by colour). Adult chickens have a fleshy crest on their heads called a comb or cockscomb, and hanging flaps of skin either side under their beaks called wattles. These organs help to cool the bird by redirecting blood flow to the skin. Both the adult male and female have wattles and combs, but in most breeds these are more prominent in males.

In the wild, chickens often scratch at the soil to search for seeds, insects and even larger animals such as lizards or young mice.

Domestic chickens are not capable of long distance flight, although lighter birds are generally capable of flying for short distances, such as over fences or into trees (where they would naturally roost). Chickens will sometimes fly to explore their surroundings, but usually do so only to flee perceived danger. Because of the risk of escape, chickens raised in open-air pens often have one of their wings clipped by the breeder—the tips of the longest feathers on one of the wings are cut, resulting in unbalanced flight which the bird cannot sustain for more than a few meters, and it is thus discouraged from flying at all.

Chickens are gregarious birds and live together as a flock. They have a communal approach to the incubation of eggs and raising of young. Individual chickens in a flock will dominate others, establishing a " pecking order," with dominant individuals having priority for access to food and nesting locations. Removing hens or roosters from a flock causes a temporary disruption to this social order until a new pecking order is established. Adding hens—especially younger birds—to an existing flock, can lead to violence and injury.

Hens will try to lay in nests that already contain eggs, and have been known to move eggs from neighbouring nests into their own. Some farmers use fake eggs made from plastic or stone (or golf balls) to encourage hens to lay in a particular location. The result of this behaviour is that a flock will use only a few preferred locations, rather than having a different nest for every bird.

Hens can also be extremely stubborn about always laying in the same location. It is not unknown for two (or more) hens to try to share the same nest at the same time. If the nest is small, or one of the hens is particularly determined, this may result in chickens trying to lay on top of each other.

Contrary to popular belief, roosters do not crow only at dawn, but may crow at any time of the day or night. Their crowing (a loud and sometimes shrill call) is a territorial signal to other roosters. However, crowing may also result from sudden disturbances within their surroundings. Hens cluck loudly after laying an egg, and also to call their chicks.

In 2006, scientists researching the ancestry of birds "turned on" a chicken recessive gene, talpid2, and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils. John Fallon, the overseer of the project, stated that chickens have "...retained the ability to make teeth, under certain conditions..."

Courting

When a rooster finds food he may call the other chickens to eat it first. He does this by clucking in a high pitch as well as picking up and dropping the food. This behaviour can also be observed in mother hens, calling their chicks. In some cases the rooster will drag the wing opposite the hen on the ground, while circling her. This is part of chicken courting ritual. When a hen is used to coming to his "call" the rooster may mount the hen and proceed with the fertilization.

Breeding

Under natural conditions most birds lay only until a clutch is complete, and they will then incubate all the eggs. Many domestic hens will also do this – and are then said to go broody. The broody hen will stop laying and instead will focus on the incubation of the eggs (a full clutch is usually about 12 eggs). She will sit or set fast on the nest, protesting or pecking in defense if disturbed or removed, and she will rarely leave the nest to eat, drink, or dust-bathe. While brooding, the hen maintains the nest at a constant temperature and humidity, as well as turning the eggs regularly during the first part of the incubation. To stimulate broodiness, an owner may place many artificial eggs in the nest, or to stop it they may place the hen in an elevated cage with an open wire floor.

At the end of the incubation period (about 21 days), the eggs, if fertile, will hatch. Development of the egg starts only when incubation begins, so they all hatch within a day or two of each other, despite perhaps being laid over a period of two weeks or so. Before hatching the hen can hear the chicks peeping inside the eggs, and will gently cluck to stimulate them to break out of their shells. The chick begins by pipping – pecking a breathing hole with its egg tooth towards the blunt end of the egg, usually on the upper side. It will then rest for some hours, absorbing the remaining egg-yolk and withdrawing the blood supply from the membrane beneath the shell (used earlier for breathing through the shell). It then enlarges the hole, gradually turning round as it goes, and eventually severing the blunt end of the shell completely to make a lid. It crawls out of the remaining shell and its wet down dries out in the warmth of the nest.

The hen will usually stay on the nest for about two days after the first egg hatches, and during this time the newly-hatched chicks live off the egg yolk they absorb just before hatching. Any eggs not fertilized by a rooster will not hatch, and the hen eventually loses interest in these and leaves the nest. After hatching the hen fiercely guards the chicks, and will brood them when necessary to keep them warm, at first often returning to the nest at night. She leads them to food and water – she will call them to edible items, but rarely feeds them directly. She continues to care for them until they are several weeks old, when she will gradually lose interest and eventually start to lay again.

Modern egg-laying breeds rarely go broody, and those that do often stop part-way through the incubation. However, some "utility" (general purpose) breeds, such as the Cochin, Cornish and Silkie, do regularly go broody, and they make excellent mothers, not only for chicken eggs but also for those of other species -- even those with much smaller or larger eggs and different incubation periods, such as quail, pheasants, turkeys or geese. Chicken eggs can also be hatched under a broody duck, with varied success.

Artificial incubation

Chicken egg incubation can successfully occur artificially as well. Nearly all fertilized Chicken eggs will hatch after 21 days of good conditions - 99.5 ° F (37.5 ° C) and around 55% relative humidity (increase to 70% in the last three days of incubation to help soften egg shell). Eggs must be turned regularly (usually three to eight times each week) during the first part of the incubation. If the eggs aren't turned, the embryo inside will stick to the shell and may hatch with physical defects. Some incubators turn the eggs automatically. This turning mimics the natural process – an incubating hen will stand up several times a day and shift the eggs around with her beak. However, if the egg is turned during the last week of incubation the chick may have difficulty settling in the correct hatching position.

Many commercial incubators are industrial-sized with shelves holding tens of thousands of eggs at a time, with rotation of the eggs a fully automated process. Home incubators are boxes holding from half a dozen to 75 eggs; they are usually electrically powered, but in the past some were heated with an oil or paraffin lamp.

Chickens as food

The meat of the chicken, also called "chicken," is a type of poultry meat. Because of its relatively low cost, chicken is one of the most used meats in the world. Nearly all parts of the bird can be used for food, and the meat can be cooked in many different ways. Popular chicken dishes include fried chicken, chicken soup, Buffalo wings, tandoori chicken, butter chicken, and chicken rice. Chicken is also a staple of fast food restaurants. Commercially produced chicken usually has a fairly neutral flavor and texture, and is used as a reference point for describing other foods; many are said to " taste like chicken" if they are indistinctive. Many people choose not to eat chicken as part of a vegetarian lifestyle.

Chickens as pets

Chickens can make good companion animals and can be tamed by hand feeding, but roosters can sometimes become aggressive. Some have advised against keeping them around very young children. Some people find chickens' behaviour entertaining and educational.

While some cities in the United States allow chickens as pets, the practice is not approved in all localities. Some communities ban only roosters, allowing the quieter hens. The so called "urban hen movement" harks back to the days when chicken keeping was much more common, and involves the keeping of small groups of hens in areas where they may not be expected, such as closely populated cities and suburban areas. City ordinances, zoning regulations or health boards may determine whether chickens may be kept. A general requirement is that the birds be confined to the owner's property, not allowed to roam freely. There may be strictures on how far from human dwellings a coop may be located, etc.

Chickens are generally low-maintenance. The major challenge is protecting the birds from predators such as dogs, raccoons and foxes. A bird left out at night is likely to be killed by a predator. Chickens are usually kept in a roost at night and a pen in the day (unless they are free-range). The floor is covered with bedding such as straw or wood shavings, which, with the high-nitrogen droppings, can go into a compost pile.

Roosters are not required, as hens still lay eggs, but these eggs are not fertilized by the rooster therefore they will not hatch. Fresh egg yolks are "perky" and float above the white. Yolk color varies. According to Gail Damerow's handbook, "Egg yolks get their colour from xanthophyll, a natural yellow-orange pigment in green plants and yellow corn, and the same pigment that colors the skin and shanks of yellow-skinned hens. The exact colour of a yolk depends on the source of the xanthophyll." A subsequent table ascribes raw yolks colored "orange to dark yellow" to "green feed, yellow corn."

If hens are allowed to forage or are fed additional greens, their eggs may differ from USDA standards. Barb Gorski, a Pennsylvania farmer of pastured poultry, had some of her chicken eggs analyzed under the USDA-supported Sustainable Agriculture Research and Education (SARE) program. According to the laboratory results, "Eggs of the pastured chickens contained 34% less cholesterol, 10% less fat, 40% more vitamin A, twice as much omega-6 fatty acid, and four times as much omega-3 fatty acid as the USDA standard."

While the bulk of a pet chickens' diet should be a balanced commercial mix, for household chickens "green feed" can be as simple as poison-free, short grass clippings from lawn mowing. Chickens will forage for chickweed and other plants, seeds, and insects.

Chickens can also consume pulverized eggshells or otherwise unused food, such as meal leavings and old (but not rotted) produce. Damerow recommends leftover baked goods, fruit, or vegetable peelings, excess milk in modest amounts; advises against making such scraps the sole diet, or including raw potato peels "which chickens can't easily digest..." or "...anything spoiled or rotten...strong-tasting foods like onions, garlic, or fish."

In Asia, chickens with striking plumage have long been kept for ornamental purposes, including feather-footed varieties such as the Cochin from Vietnam, the Silkie from China, and the extremely long-tailed Phoenix from Japan. Asian ornamental varieties were imported into the United States and Great Britain in the late 1800s. Distinctive American varieties of chickens have been developed from these Asian breeds. Poultry fanciers began keeping these ornamental birds for exhibition, a practice that continues today. Individuals in rural communities commonly keep chickens for both ornamental and practical value. Zoos sometimes use chickens instead of insecticides to control insect populations.

Chickens in agriculture

In the United States, chickens were raised primarily on family farms until roughly 1960. Originally, the primary value in poultry keeping was eggs, and meat was considered a byproduct of egg production. Its supply was less than the demand, and poultry was expensive. Except in hot weather, eggs can be shipped and stored without refrigeration for some time before going bad; this was important in the days before widespread refrigeration.

Farm flocks tended to be small because the hens largely fed themselves through foraging, with some supplementation of grain, scraps, and waste products from other farm ventures. Such feedstuffs were in limited supply, especially in the winter, and this tended to regulate the size of the farm flocks. Soon after poultry keeping gained the attention of agricultural researchers (around 1896), improvements in nutrition and management made poultry keeping more profitable and businesslike.

Prior to about 1910, chicken was served primarily on special occasions or Sunday dinner. Poultry was shipped live or killed, plucked, and packed on ice (but not eviscerated). The "whole, ready-to-cook broiler" wasn't popular until the Fifties, when end-to-end refrigeration and sanitary practices gave consumers more confidence. Before this, poultry were often cleaned by the neighbourhood butcher, though cleaning poultry at home was a commonplace kitchen skill.

Two kinds of poultry were generally offered: broilers or "spring chickens," young male chickens, a byproduct of the egg industry, which were sold when still young and tender (generally under 3 pounds live weight); and "fowls" or "stewing hens," also a byproduct of the egg industry, which were old hens past their prime for laying. This is no longer practiced; modern meat chickens are a different breed. Egg-type chicken carcasses no longer appear in stores.

The major milestone in 20th century poultry production was the discovery of Vitamin-D (named in 1922), which made it possible to keep chickens in confinement year-round. Before this, chickens did not thrive during the winter (due to lack of sunlight), and egg production, incubation, and meat production in the off-season were all very difficult, making poultry a seasonal and expensive proposition. Year-round production lowered costs, especially for broilers.

At the same time, egg production was increased by scientific breeding. After a few false starts, such as the Maine Experiment Station's failure at improving egg production, success was shown by Professor Dryden at the Oregon Experiment Station.

Improvements in production and quality were accompanied by lower labor requirements. In the Thirties through the early Fifties, 1,500 hens was considered to be a full-time job for a farm family. In the late Fifties, egg prices had fallen so dramatically that farmers typically tripled the number of hens they kept, putting three hens into what had been a single-bird cage or converting their floor-confinement houses from a single deck of roosts to triple-decker roosts. Not long after this, prices fell still further and large numbers of egg farmers left the business. This marked the beginning of the transition from family farms to larger, vertically integrated operations.

Robert Plamondon reports that the last family chicken farm in his part of Oregon, Rex Farms, had 30,000 layers and survived into the Nineties. But the standard laying house of the surviving operations is around 125,000 hens.

This fall in profitability was accompanied by a general fall in prices to the consumer, allowing poultry and eggs to lose their status as luxury foods.

The vertical integration of the egg and poultry industries was a late development, occurring after all the major technological changes had been in place for years (including the development of modern broiler rearing techniques, the adoption of the Cornish Cross broiler, the use of laying cages, etc.).

By the late Fifties, poultry production had changed dramatically. Large farms and packing plants could grow birds by the tens of thousands. Chickens could be sent to slaughterhouses for butchering and processing into prepackaged commercial products to be frozen or shipped fresh to markets or wholesalers. Meat-type chickens currently grow to market weight in six to seven weeks whereas only fifty years ago it took three times as long. This is due to genetic selection and nutritional modifications (and not the use of growth hormones, which are illegal for use in poultry in the US and many other countries). Once a meat consumed only occasionally, the common availability and lower cost has made chicken a common meat product within developed nations. Growing concerns over the cholesterol content of red meat in the 1980s and 1990s further resulted in increased consumption of chicken.

Today, eggs are produced on large egg ranches on which environmental parameters are controlled. Chickens are exposed to artificial light cycles to stimulate egg production year-round. In addition, it is a common practice to induce molting through manipulation of light and the amount of food they receive in order to further increase egg size and production.

On average, a chicken lays one egg a day for a number of days (a "clutch"), then does not lay for one or more days, then lays another clutch. Originally, the hen presumably laid one clutch, became broody, and incubated the eggs. Selective breeding over the centuries has produced hens that lay more eggs than they can hatch. Some of this progress was ancient, but most occurred after 1900. In 1900, average egg production was 83 eggs per hen per year. In 2000, it was well over 300.

In the United States, laying hens are butchered after their second egg laying season. In Europe, they are generally butchered after a single season. The laying period begins when the hen is about 18-20 weeks old (depending on breed and season). Males of the egg-type breeds have little commercial value at any age, and all those not used for breeding (roughly fifty percent of all egg-type chickens) are killed soon after hatching. Such "day-old chicks" are sometimes sold as food for captive and falconers birds of prey. The old hens also have little commercial value. Thus, the main sources of poultry meat a hundred years ago (spring chickens and stewing hens) have both been entirely supplanted by meat-type broiler chickens.

Traditionally, chicken production was distributed across the entire agricultural sector. In the twentieth century, it gradually moved closer to major cities to take advantage of lower shipping costs. This had the undesirable side effect of turning the chicken manure from a valuable fertilizer that could be used profitably on local farms to an unwanted byproduct. This trend may be reversing itself due to higher disposal costs on the one hand and higher fertilizer prices on the other, making farm regions attractive once more.

From the farmer's point of view, eggs used to be practically the same as currency, with general stores buying eggs for a stated price per dozen. Egg production peaks in the early spring, when farm expenses are high and income is low. On many farms, the flock was the most important source of income, though this was often not appreciated by the farmers, since the money arrived in many small payments. Eggs were a farm operation where even small children could make a valuable contribution.

Distribution

FAO reports that China was the top chicken market in 2004 followed by the USA.

Issues with mass production

Humane treatment

Animal welfare groups have frequently targeted the poultry industry for engaging in practices which they believe to be inhumane. Many animal welfare advocates object to killing chickens for food, the " factory farm conditions" under which they are raised, methods of transport, and slaughter. PETA and other groups have repeatedly conducted undercover investigations at chicken farms and slaughterhouses which they allege confirm their claims of cruelty.

Laying hens are routinely debeaked to prevent fighting. Because beaks are sensitive, trimming them without anaesthesia is considered inhumane by some. It is also argued that the procedure causes life-long discomfort. Conditions in intensive chicken farms may be unsanitary, allowing the proliferation of diseases such as salmonella and E coli. Chickens may be raised in total darkness. Rough handling and crowded transport during various weather conditions and the failure of existing stunning systems to render the birds unconscious before slaughter have also been cited as welfare concerns.

Another animal welfare concern is the use of selective breeding to create heavy, large-breasted birds, which can lead to crippling leg disorders and heart failure for some of the birds. Concerns have been raised that companies growing single varieties of birds for eggs or meat are increasing their susceptibility to disease.

Some groups who advocate for more humane treatment of chickens, claim that they are intelligent. Dr. Chris Evans of Macquarie University claims that their range of 20 calls, problem solving skills, use of representational signalling, and the ability to recognize each other by facial features demonstrate the intelligence of chickens. .

In 2004, 8.9 billion chickens were slaughtered in the United States. There is no federal law that regulates the humane treatment of chickens.

Human concerns

Antibiotics

Antibiotics have been used on poultry in large quantities since the Forties, when it was found that the byproducts of antibiotic production, fed because the antibiotic-producing mold had a high level of vitamin B12 after the antibiotics were removed, produced higher growth than could be accounted for by the vitamin B12 alone. Eventually it was discovered that the trace amounts of antibiotics remaining in the byproducts accounted for this growth.

The mechanism is apparently the adjustment of intestinal flora, favoring "good" bacteria while suppressing "bad" bacteria, and thus the goal of antibiotics as a growth promoter is the same as for probiotics. Because the antibiotics used are not absorbed by the gut, they do not put antibiotics into the meat or eggs.

Antibiotics are used routinely in poultry for this reason, and also to prevent and treat disease. Many contend that this puts humans at risk as bacterial strains develop stronger and stronger resistances. Critics point out that, after six decades of heavy agricultural use of antibiotics, opponents of antibiotics must still make arguments about theoretical risks, since actual examples are hard to come by. Those antibiotic-resistant strains of human diseases whose origin is known originated in hospitals rather than farms.

A proposed bill in the American congress would make the use of antibiotics in animal feed legal only for therapeutic (rather than preventative) use, but it has not been passed yet. However, this may present the risk of slaughtered chickens harboring pathogenic bacteria and passing them on to humans that consume them.

In October 2000, the FDA discovered that two antibiotics were no longer effective in treating diseases found in factory-farmed chickens; one antibiotic was swiftly pulled from the market, but the other, Baytril was not. Bayer, the company which produced it, contested the claim and as a result, Baytril remained in use until July 2005.

Arsenic

Chicken feed can also include Roxarsone, an antimicrobial drug that also promotes growth. The drug has generated controversy because it contains the element arsenic, which can cause cancer, dementia, and neurological problems in humans. Yet the arsenic in Roxarsone is not of the type which has been linked to cancer. A Consumer Reports study in 2004 reported finding "no detectable arsenic in our samples of muscle" but found "A few of our chicken-liver samples has an amount that according to EPA standards could cause neurological problems in a child who ate 2 ounces of cooked liver per week or in an adult who ate 5.5 ounces per week." However, the Food and Drug Administration (FDA) is the organization responsible for the regulation of foods in America, and all samples tested were "far less than the... amount allowed in a food product."

Growth hormones

Chickens grow much more rapidly than they once did and some consumers have concluded that this rapid growth is due to the use of hormones in these animals. Some consumers believe that the increasingly earlier onset of puberty in humans is the result of the liberal use of such hormones. However, hormone use in poultry production is illegal in the United States. Similarly, no chicken meat for sale in Australia is fed hormones. Furthermore, several scientific studies have documented the fact that chickens grow rapidly because they are bred to do so. A small producer of natural and organic chickens confirmed this assumption:

“

If this were 1948, you might have something to worry about. Using hormones to boost egg production was a brief fad in the Forties, but was abandoned because it didn't work. Using hormones to produce soft-meated roasters was used to some extent in the Forties and Fifties, but the increased growth rates of broilers made the practice irrelevant--the broilers got as big as anyone wanted them to get when they were still young enough to be soft-meated without chemicals. The only hormone that was ever used in any quantity on poultry (DES) was banned in 1959, after everyone but a few die-hard farmers had given them up as a silly idea. Hormones are now illegal in poultry and eggs. The people who advertise "No hormones" are either woefully ignorant or are indulging in cynical fear-mongering, maybe both.

”

E. coli

According to Consumer Reports, "1.1 million or more Americans [are] sickened each year by undercooked, tainted chicken." A USDA study discovered E. coli in 99% of supermarket chicken, the result of chicken butchering not being a sterile process. Feces tend to leak from the carcass until the evisceration stage, and the evisceration stage itself gives an opportunity for the interior of the carcass to receive intestinal bacteria. (So does the skin of the carcass, but the skin presents a better barrier to bacteria and reaches higher temperatures during cooking). Before 1950, this was contained largely by not eviscerating the carcass at the time of butchering, deferring this until the time of retail sale or in the home. This gave the intestinal bacteria less opportunity to colonize the edible meat. The development of the "ready-to-cook broiler" in the 1950s added convenience while introducing risk, under the assumption that end-to-end refrigeration and thorough cooking would provide adequate protection. E. coli can be killed by proper cooking times, but there is still some risk associated with it, and its near-ubiquity in commercially-farmed chicken is troubling to some. Irradiation has been proposed as a means of sterilizing chicken meat after butchering.

Avian influenza

There is also a risk that the crowded conditions in many chicken farms will allow avian influenza to spread quickly. A United Nations press release states: "Governments, local authorities and international agencies need to take a greatly increased role in combating the role of factory-farming, commerce in live poultry, and wildlife markets which provide ideal conditions for the virus to spread and mutate into a more dangerous form..."

Efficiency

Farming of chickens on an industrial scale relies largely on high protein feeds derived from soybeans; in the European Union the soybean dominates the protein supply for animal feed, and the poultry industry is the largest consumer of such feed. Giving the feed to chickens means the protein reaches humans with a much lower efficiency than through direct consumption of soybean products. Some nutrients, however, are present in chicken but not in the soybean.

Genetic Pollution

One other major problem concerns the wild Red Junglefowl. Feral populations of domestic birds may stray across the ranges of the wild Junglefowl species, it has created a concern of genetic pollution. Wild Junglefowl should have an eclipse plumage but apparently some males lack such a plumage, indicating hybridisation with the domestic chicken. Further confusing the issue of hybrids is that the domestic chicken itself is a hybrid between the Red and Grey Junglefowl. It has even been suggested that pure populations of Red Junglefowl may already be extinct.

Chicken diseases

Chickens are susceptible to several parasites, including lice, mites, ticks, fleas, and intestinal worms, as well as other diseases. (Despite the name, they are not affected by Chickenpox; that is a disease of humans, not chickens.)

Some of the common diseases that affect chickens are shown below:

Name	Common Name	Caused by
Aspergillosis		fungi
Avian influenza	bird flu	virus
Histomoniasis	Blackhead disease	protozoal parasite
Botulism		toxin
Cage Layer Fatigue		mineral deficiencies, lack of exercise
Coccidiosis		parasites
Colds		virus
Crop Bound		improper feeding
Dermanyssus gallinae	Red mite	parasite
Egg bound		oversized egg
Erysipelas		bacteria
Fatty Liver Hemorrhagic Syndrome		high-energy food
Fowl Cholera		bacteria
Fowl pox		virus
Fowl Typhoid		bacteria
Gallid herpesvirus 1 or Infectious Laryngotracheitis		virus
Gapeworm	Syngamus trachea	worms
Infectious Bronchitis		virus
Infectious Bursal Disease	Gumboro	virus
Infectious Coryza		bacteria
Lymphoid leukosis		Avian leukosis virus
Marek's disease		virus
Moniliasis	Yeast Infection or Thrush	fungi
Mycoplasmas		bacteria-like organisms
Newcastle disease		virus
Necrotic Enteritis		bacteria
Omphalitis	Mushy chick disease	umbilical cord stump
Prolapse
Psittacosis		bacteria
Pullorum	Salmonella	bacteria
Scaly leg		parasites
Squamous cell carcinoma		cancer
Tibial dyschondroplasia		speed growing
Toxoplasmosis		protozoal parasite
Ulcerative Enteritis		bacteria

Chickens in religion

In Islam, The Messenger of Allah said, "When you hear the crowing of cocks, ask for Allah's Blessings for (their crowing indicates that) they have seen an angel. And when you hear the braying of donkeys, seek Refuge with Allah from Satan for (their braying indicates) that they have seen a Satan." Sahih Al-Bukhari Vol. 4, Book 54, Number 522: Narrated Abu Huraira.

In Indonesia the chicken has great significance during the Hindu cremation ceremony. A chicken is considered a channel for evil spirits which may be present during the ceremony. A chicken is tethered by the leg and kept present at the ceremony for its duration to ensure that any evil spirits present during the ceremony go into the chicken and not the family members present. The chicken is then taken home and returns to its normal life.

In ancient Greece, the chicken was not normally used for sacrifices, perhaps because it was still considered an exotic animal. Because of its valour, the cock is found as an attribute of Ares, Heracles, and Athena. The alleged last words of Socrates as he died from hemlock poisoning, as recounted by Plato, were " Crito, I owe a cock to Asclepius; will you remember to pay the debt?", signifying that death was a cure for the illness of life.

The Greeks believed that even lions were afraid of cocks. Several of Aesop's Fables reference this belief. In the cult of Mithras, the cock was a symbol of the divine light and a guardian against evil.

In the New Testament, Jesus prophesied the betrayal by Peter: "Jesus answered, 'I tell you, Peter, before the rooster crows today, you will deny three times that you know me.'" ( Luke 22:34) Thus it happened ( Luke 22:61), and Peter cried bitterly. This made the cock a symbol for both vigilance and betrayal.

Earlier, Jesus compares himself to a mother hen when talking about Jerusalem: "O Jerusalem, Jerusalem, you who kill the prophets and stone those sent to you, how often I have longed to gather your children together, as a hen gathers her chicks under her wings, but you were not willing." ( Matthew 23:37; also Luke 13:34).

In many Central European folk tales, the devil is believed to flee at the first crowing of a cock.

In traditional Jewish practice, a chicken is swung around the head and then slaughtered on the afternoon before Yom Kippur, the Day of Atonement, in a ritual called kapparos. The sacrifice of the chicken is to receive atonement, for the bird takes on all the person's sins in kapparos. The meat is then donated to the poor. A woman brings a hen for the ceremony, while a man brings a rooster. Although not actually a sacrifice in the biblical sense, the death of the chicken reminds the penitent sinner that his or her life is in God's hands.

The Talmud speaks of learning "courtesy toward one's mate" from the rooster. This might refer to the fact that when a rooster finds something good to eat, he calls his hens to eat first.

The chicken is one of the Zodiac symbols of the Chinese calendar. Also in Chinese religion, a cooked chicken as a religious offering is usually limited to ancestor veneration and worship of village deities. Vegetarian deities such as the Buddha are not one of the recipients of such offerings. Under some observations, an offering of chicken is presented with "serious" prayer (while roasted pork is offered during a joyous celebration). In Confucian Chinese Weddings, a chicken can be used as a substitute for one who is seriously ill or not available (e.g sudden death) to attend the ceremony. A red silk scarf is placed on the chicken's head and a close relative of the absent bride/groom holds the chicken so the ceremony may proceed. However, this practice is rare today.

Chickens in history

The first pictures of chickens in Europe are found on Corinthian pottery of the 7th century BCE. The poet Cratinus (mid-5th century BCE, according to the later Greek author Athenaeus) calls the chicken "the Persian alarm". In Aristophanes's comedy The Birds (414 BCE) a chicken is called "the Median bird", which points to an introduction from the East. Pictures of chickens are found on Greek red figure and black-figure pottery.

In ancient Greece, chickens were still rare and were a rather prestigious food for symposia. Delos seems to have been a centre of chicken breeding.

An early domestication of chickens in Southeast Asia is probable, since the word for domestic chicken (*manuk) is part of the reconstructed Proto-Austronesian language (see Austronesian languages). Chickens, together with dogs and pigs, were the domestic animals of the Lapita culture, the first Neolithic culture of Oceania.

Chickens were spread by Polynesian seafarers and reached Easter Island in the 12th century BCE, where they were the only domestic animal, with the possible exception of the Polynesian Rat (Rattus exulans). They were housed in extremely solid chicken coops built from stone. Traveling as cargo on trading boats, they reached the Asian continent via the islands of Indonesia and from there spread west to Europe and western Asia.

The Romans used chickens for oracles, both when flying ("ex avibus") and when feeding ("auspicium ex tripudiis"). The hen ("gallina") gave a favourable omen ("auspicium ratum"), when appearing from the left (Cic.,de Div. ii.26), like the crow and the owl.

For the oracle "ex tripudiis" according to Cicero (Cic. de Div. ii.34), any bird could be used, but normally only chickens ("pulli") were consulted. The chickens were cared for by the pullarius, who opened their cage and fed them pulses or a special kind of soft cake when an augury was needed. If the chickens stayed in their cage, made noises ("occinerent"), beat their wings or flew away, the omen was bad; if they ate greedily, the omen was good.

In 249 BCE, the Roman general Publius Claudius Pulcher had his chickens thrown overboard when they refused to feed before the battle of Drepana, saying "If they won't eat, perhaps they will drink." He promptly lost the battle against the Carthaginians and 93 Roman ships were sunk. Back in Rome, he was tried for impiety and heavily fined.

In 161 BCE a law was passed in Rome that forbade the consumption of fattened chickens. It was renewed a number of times, but does not seem to have been successful. Fattening chickens with bread soaked in milk was thought to give especially delicious results. The Roman gourmet Apicius offers 17 recipes for chicken, mainly boiled chicken with a sauce. All parts of the animal are used: the recipes include the stomach, liver, testicles and even the pygostyle (the fatty "tail" of the chicken where the tail feathers attach).

The Roman author Columella gives advice on chicken breeding in his eighth book of his treatise on agriculture. He identifies Tanagrian, Rhodic, Chalkidic and Median (commonly misidentified as Melian) breeds, which have an impressive appearance, a quarrelsome nature and were used for cockfighting by the Greeks. For farming, native (Roman) chickens are to be preferred, or a cross between native hens and Greek cocks. Dwarf chickens are nice to watch because of their size but have no other advantages.

Per Columella, the ideal flock consists of 200 birds, which can be supervised by one person if someone is watching for stray animals. White chickens should be avoided as they are not very fertile and are easily caught by eagles or goshawks. One cock should be kept for five hens. In the case of Rhodian and Median cocks that are very heavy and therefore not much inclined to sex, only three hens are kept per cock. The hens of heavy fowls are not much inclined to brood; therefore their eggs are best hatched by normal hens. A hen can hatch no more than 15-23 eggs, depending on the time of year, and supervise no more than 30 hatchlings. Eggs that are long and pointed give more male, rounded eggs mainly female hatchlings.

Per Columella, chicken coops should face southeast and lie adjacent to the kitchen, as smoke is beneficial for the animals. Coops should consist of three rooms and possess a hearth. Dry dust or ash should be provided for dust-baths.

According to Columella, chicken should be fed on barley groats, small chick-peas, millet and wheat bran, if they are cheap. Wheat itself should be avoided as it is harmful to the birds. Boiled ryegrass (Lollium sp.) and the leaves and seeds of alfalfa (Medicago sativa L.) can be used as well. Grape marc can be used, but only when the hens stop laying eggs, that is, about the middle of November; otherwise eggs are small and few. When feeding grape marc, it should be supplemented with some bran. Hens start to lay eggs after the winter solstice, in warm places around the first of January, in colder areas in the middle of February. Parboiled barley increases their fertility; this should be mixed with alfalfa leaves and seeds, or vetches or millet if alfalfa is not at hand. Free-ranging chickens should receive two cups of barley daily.

Columella advises farmers to slaughter hens that are older than three years, because they no longer produce sufficient eggs.

Capons were produced by burning out their spurs with a hot iron. The wound was treated with potter's chalk.

For the use of poultry and eggs in the kitchens of ancient Rome see Roman eating and drinking.

Chickens in South America

An unusual variety of chicken that has its origins in South America is the araucana. Araucanas, some of which are tailless and some of which have tufts of feathers around their ears, lay blue-green eggs. It has long been suggested that they predate the arrival of European chickens brought by the Spanish and are evidence of pre-Columbian trans-Pacific contacts between Asian or Pacific Oceanic peoples, particularly the Polynesians and South America. In 2007, an international team of researchers reported the results of analysis of chicken bones found on the Arauco Peninsula in south central Chile. Radiocarbon dating indicated that the chickens were Pre-Columbian, and DNA analysis showed that they were related to prehistoric populations of chickens in Polynesia. These results appear to confirm that the chickens came from Polynesia and that there were transpacific contacts between Polynesia and South America before Columbus's arrival in the Americas.