Emily Carter
Chickens, scientifically known as Gallus gallus domesticus, are one of the most common and widespread domesticated animals in the world, with a global population of over 26.5 billion as of 2023. They are primarily kept for their meat and eggs, but some people also keep them as pets. Chickens are social, intelligent, and inquisitive birds, and their economic importance makes them a central component of global animal husbandry and agriculture. Given their widespread domestication, it is important to be able to perform a physical examination on a chicken to prevent or limit the spread of disease among flocks. This involves restraining the bird, examining its head and neck, checking its eyes, beak, mouth, feathers, and underlying skin for any abnormalities, palpating its breast muscles, and collecting blood samples.
| Characteristics | Values |
|---|---|
| Scientific Name | Gallus gallus domesticus |
| Subspecies Of | Red junglefowl (Gallus gallus) |
| First Domesticated | c. 6000 BC |
| Number of Breeds | Over 400 |
| Population | 26.5 billion+ (as of 2023) |
| Annual Production | 50 billion+ |
| Use | Meat, eggs, pets |
| Behaviour | Social, complex vocalisations |
| Physical Appearance | Rounded, unfeathered legs, short wings |
| Weight | 2.6 kg (5.7 lbs) on average |
| Height | Less than 70 cm (27.6 inches) |
| Examination | Restrain the bird, check for abnormal behaviour, perform oral exam, check feathers and skin, examine head and neck |
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What You'll Learn
Chicken domestication history
The chicken, scientifically known as Gallus gallus domesticus, is a domesticated subspecies of the red junglefowl (Gallus gallus), which is still found in the wild in Southeast Asia and Oceana. The red junglefowl is considered the main ancestor of the domestic chicken, and chickens have also interbred with populations of grey junglefowl, Sri Lankan junglefowl, and green junglefowl. Chickens share between 71 and 79% of their genome with red junglefowl.
It is believed that chickens were first domesticated around 8,000 years ago, although the exact timing and location of their domestication is still debated. Some sources suggest that chickens were first tamed in China around 6000 BC, with other evidence pointing to earlier domestication in Southeast Asia. Archaeological evidence supports the presence of domestic chickens in Southeast Asia well before 6000 BC, and by 2000 BC in China and India.
Chickens were likely initially kept for cockfighting, and only later became a primary source of meat and eggs. They were widespread throughout southern Central Asia by the 4th century BC, and were also present in the Middle East around this time, with remains found in Syria dating back to around 2000 BC. During the Hellenistic period (4th-2nd centuries BC), chickens began to be widely domesticated for food in the southern Levant. The Phoenicians spread chickens along the Mediterranean coasts as far as Iberia, and the first pictures of chickens in Europe are found on Corinthian pottery from the 7th century BC.
Breeding increased under the Roman Empire, and chickens became one of the most common and widespread domesticated animals in the world. Today, the global chicken population exceeds 26.5 billion, with more than 50 billion birds produced annually for consumption.
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Physical examination techniques
Restraining the Bird:
When restraining a chicken for examination, it is important to keep the bird calm and minimise stress. Reach over the bird's back, hold its wings folded close to its body, and then pick it up by inserting your fingers between its legs while supporting its breastbone with your other hand. Avoid restraining the bird upside down, as this can increase stress and the risk of regurgitation and broken bones. If the bird appears stressed, cover its head with light linen until it calms down.
Sanitation and Biosecurity:
Practising good sanitation and biosecurity is crucial. Wear disposable gloves during the examination and wash your hands and garments afterwards. If you suspect illness, isolate the bird from the rest of the flock to prevent disease transmission. Some poultry diseases can affect humans even if the bird shows no symptoms.
Palpation of Breast Muscles:
Palpating the breast muscles on either side of the keel is an important technique. This can be done by briefly suspending the bird upside down or palpating it while it sits normally. Use your dominant hand in a "V" shape to feel both left and right muscles simultaneously. Assess the muscle tone—they should be full and firm. The degree of muscling can indicate the bird's body condition, and a prominent breastbone may suggest chronic weight loss or disease. Note that breast muscling varies between breeds.
Head and Neck Examination:
The head and neck examination should include checking the comb, eyes, external nares, and beak. The comb should be bright red, slightly warm, free of scabs and lesions, and turgid. Observe the eyes for any discharge or cloudiness, which can indicate illness. Check the eyelids for swelling, and ensure they are open wide. The external nares should be inspected for discharge, crusts, and scratches. The beak should be smooth, pointed, and free of cracks.
Oral Examination:
Open the bird's mouth and examine the tongue and mucosal membranes for ulcers or lesions. Check the colour of a hen's earlobes to predict the future egg colour. The choanal cleft, a naturally cleft hard palate, is an ideal spot for sampling respiratory bacteria and viruses. Blunted papillae in this area indicate poor nutrition and a lack of vitamin A.
Feather and Skin Evaluation:
Evaluate the feathers and underlying skin. Part the feathers to check for parasites, lice, and mites. The feathers should lie flat and be well-preened. Check the base of the feather shaft for any lice eggs (nits) and ensure it is free of parasites.
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Chicken anatomy
Chickens are relatively large, round-bodied, active, diurnal birds. They are primarily kept for their meat and eggs, though they are also kept as pets. Chickens are social, inquisitive, and intelligent birds, and their economic importance makes them a central component of global animal husbandry and agriculture.
The chicken's head has several parts, including a comb, wattles, earlobes, and an eyeball. Combs and wattles are red, soft, and warm. Chickens do not have external ears like humans; instead, they have openings into the ear canal protected by a covering of feathers. The earlobe colour depends on the breed and can be red or white. The eyeball is covered by the eye ring, which appears as a ring of skin when the eye is open.
The chicken's beak is an essential part of its anatomy, as it uses its beak to move and pick up food. Inside the beak is a barbed, triangular tongue that helps move food backward toward the oesophagus. The tongue also aids in tasting food and making different noises.
The crop is a muscular bag at the bottom of the chicken's neck that stores food, treats, bugs, and grass. It should be empty and flat in the mornings, filling up throughout the day and taking on the shape of a small ball. The food then passes into the gizzard overnight, where it is ground and mixed with the help of small gravel and grit that the bird has swallowed.
The oviduct is a tube along the backbone connecting the ovary and the tail, where egg development occurs. It is about 25 to 27 inches long and consists of five sections: the infundibulum, magnum, isthmus, shell gland, and vagina.
Chickens have three types of muscles: smooth, cardiac, and skeletal. Smooth muscles are found in the blood vessels, gizzard, intestines, and organs, while cardiac muscles are specialised for the heart. Skeletal muscles give the chicken its shape and enable voluntary movement, and they are the type of muscle consumed as poultry meat.
The chicken's thigh is the upper part of the leg, ending at the lower leg or drumstick. The thigh connects to the shank (foot) at the hock joint, equivalent to the human ankle. Chickens stand and walk on their toes, with most breeds having three toes projecting forward and one backward, sometimes called the claw. Some breeds have five toes, and a few have feathers on their shanks and toes.
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Chicken behaviour
Chickens are social, inquisitive, and intelligent birds, and their complex behaviours can be entertaining to humans. They are primarily kept for their meat and eggs, but they are also kept as pets.
Chickens are active during the day and spend around 61% of their time on foraging and feeding behaviours. They are highly motivated to forage for food, even when it is not necessary, and this is called contra-freeloading. Foraging behaviours include scratching and pecking at the ground to find food sources. Chickens may also roam to find places to take a dust bath or create a nest. Scratching at the ground is an instinctual behaviour, and it can also be done to create a dust bath or a nest.
Chickens do not have teeth or lips, so they use their beaks to tear off bits of food. Their tongues are barbed to help move food back towards the oesophagus. Food is stored briefly in a small pouch called a crop before moving into the stomach. From there, the food moves into the muscular gizzard, which is used to crush and grind the food, with the help of small amounts of gravel and grit that the bird has swallowed.
Chickens also perform comfort behaviours, or behaviours related to body care and maintenance, such as dust bathing, preening, leg and wing stretching, wing flapping, and tail wagging. Preening is the chicken's way of grooming itself and ensuring its feathers are in good condition. It is a social behaviour, and chickens are often seen preening synchronously as a larger group. During preening, the chicken removes any debris or external parasites within its plumage. Another part of preening is oiling the feathers, where the bird takes oil from its preen gland into its beak and distributes it along the feathers. Preening and oiling help keep feathers healthy and provide insulation and waterproofing.
Chickens are naturally curious, and they enjoy roaming to forage for food. Roaming can also help chickens relieve stress, as constantly being in close quarters with other chickens can cause stress, aggressive behaviour, and even illness.
Chickens also have mating behaviours. When a rooster wants to mate, he will find some food, pick it up and drop it repeatedly, while calling to the nearby hens. This is sometimes called "taking her out to dinner". He will then do the chicken dance, which involves dropping a wing and circling around the hen until she either squats in submission or walks away.
Finally, chickens have a hierarchical social system in which they organise themselves into ranks, known as the "pecking order".
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Chicken farming methods
Chicken farming, or poultry farming, is the raising of chickens domestically or commercially, primarily for meat and eggs, but also for feathers. Chickens are common and widespread domestic animals, with a total population of 23.7 billion as of 2018. More than 50 billion chickens are reared annually, with over 8 billion of those slaughtered each year in the United States alone for meat.
Conventional Chicken Farming
The conventional chicken farming industry typically focuses on reducing costs and maximising production through weight gain, feed efficiency, and more. This often involves keeping lights low for broilers to reduce activity. The light level is usually so low that it is difficult to read.
Organic Chicken Farming
Organic poultry production systems, on the other hand, raise birds without cages, allowing outdoor access and feeding them organic feed. Organic farming focuses on animal health and welfare, good environmental practices, and product quality. This method avoids agrochemicals such as synthetic pesticides and fertilisers.
Regenerative Chicken Farming
Regenerative chicken farming is an agricultural approach that aims to rejuvenate and improve the ecosystems in which poultry is raised, rather than depleting the land and its resources. This method prioritises soil health, creating a nutrient-rich environment for plants, which in turn benefits the chickens.
Health and Disease Control
Whether conventional, organic, or regenerative, all chicken farming methods must consider the health and disease control of their flocks. Chickens are susceptible to various diseases, including bird flu, fowl typhoid, pullorum, and fowl cholera. To prevent the spread of disease, it is important to keep the chickens' environment as clean as possible. Antibiotics are also used to stimulate appetite, control harmful bacteria, and prevent disease.
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