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A broiler (Gallus gallus domesticus) is any chicken that is bred and raised specifically for meat production. [1] Many typical broilers have white feathers and yellowish skin. Most commercial broilers reach slaughter-weight between four [2] and seven weeks of age, although slower growing breeds reach slaughter-weight at approximately 14 weeks of age. Due to extensive breeding selection for rapid early growth and the husbandry used to sustain this, broilers are susceptible to several welfare concerns, particularly skeletal malformation and dysfunction, skin and eye lesions and congestive heart conditions. Management of ventilation, housing, stocking density and in-house procedures must be evaluated regularly to support good welfare of the flock. The breeding stock (broiler-breeders) do grow to maturity but also have their own welfare concerns related to the frustration of a high feeding motivation and beak trimming. Broilers are usually grown as mixed-sex flocks in large sheds under intensive conditions.

Chicken domesticated bird, primarily a source of food or food

The chicken is a type of domesticated fowl, a subspecies of the red junglefowl. It is one of the most common and widespread domestic animals, with a total population of more than 19 billion as of 2011. There are more chickens in the world than any other bird or domesticated fowl. Humans keep chickens primarily as a source of food and, less commonly, as pets. Originally raised for cockfighting or for special ceremonies, chickens were not kept for food until the Hellenistic period.

Meat Animal flesh eaten as food

Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since prehistoric times. The advent of civilization allowed the domestication of animals such as chickens, sheep, rabbits, pigs and cattle. This eventually led to their use in meat production on an industrial scale with the aid of slaughterhouses.


Modern breeding

Before the development of modern commercial meat breeds, broilers were mostly young male chickens culled from farm flocks. Pedigree breeding began around 1916. [3] Magazines for the poultry industry existed at this time. [3] [4] A crossbred variety of chicken was produced from a male of a naturally double-breasted Cornish strain, and a female of a tall, large-boned strain of white Plymouth Rocks. [5] This first attempt at a meat crossbreed was introduced in the 1930s and became dominant in the 1960s. The original crossbreed was plagued by problems of low fertility, slow growth and disease susceptibility.

Crossbreed half-bred animal

A crossbreed is an organism with purebred parents of two different breeds, varieties, or populations. Crossbreeding, sometimes called "designer crossbreeding", is the process of breeding such an organism, often with the intention to create offspring that share the traits of both parent lineages, or producing an organism with hybrid vigor. While crossbreeding is used to maintain health and viability of organisms, irresponsible crossbreeding can also produce organisms of inferior quality or dilute a purebred gene pool to the point of extinction of a given breed of organism.

Modern broilers have become very different from the Cornish/Rock crossbreed. As an example, Donald Shaver (originally a breeder of egg-production-breeds) began gathering breeding stock for a broiler program in 1950. Besides the breeds normally favoured, Cornish Game, Plymouth Rock, New Hampshire, Langshans, Jersey Black Giant and Brahmas were included. A white feathered female line was purchased from Cobb. A full scale breeding program was commenced in 1958, with commercial shipments in Canada and the US in 1959 and in Europe in 1963. [6]

Donald McQueen Shaver was a Canadian pioneer in the poultry industry, who founded a breeding company that achieved worldwide prominence. At its peak Shaver Poultry Breeding Farms was the world's largest, being one of only two "world class foundation breeding" companies in Canada. Shaver died in 2018 of age related causes.

The Croad Langshan is an old, heavy, soft-feathered chicken breed which probably originated in China.

Brahma chicken American breed of chicken

The Brahma is a large breed of chicken developed in the United States from birds imported from the Chinese port of Shanghai. The Brahma was the principal meat breed in the United States from the 1850s until about 1930.

As a second example, colour sexing broilers was proposed by Shaver in 1973. The genetics were based on the company's breeding plan for egg-layers which had been developed in the mid-1960s. A difficulty facing the breeders of the colour-sexed broiler is that the chicken must be white-feathered by slaughter age. After 12 years, accurate colour sexing without compromising economic traits was achieved. [6]

Artificial insemination

Artificial insemination is a mechanism in which spermatozoa are deposited into the reproductive tract of a female. [7] Artificial insemination provides a number of benefits relating to reproduction in the poultry industry. Broiler breeds have been selected specifically for growth, causing them to develop large pectoral muscles, which interfere with and reduce natural mating. [8] The amount of sperm produced and deposited in the hen’s reproductive tract may be limited because of this. Additionally, the males overall sex drive may be significantly reduced due to growth selection. [9] Artificial insemination has also allowed many farmers to incorporate selected genes into their stock, increasing their genetic quality [10]

Abdominal massage is the most common method used for semen collection. [8] During this process, the rooster is restrained and the back region located towards the tail and behind the wings is caressed. This is done gently but quickly. Within a short period of time, the male should get an erection of the phallus. Once this occurs, the cloaca is squeezed and semen is collected from the external papilla of the vas deferens [11]

During artificial insemination, semen is most frequently deposited intra-vaginally by means of a plastic syringe. In order for semen to be deposited here, the vaginal orifice is everted through the cloaca. This is simply done by applying pressure to the abdomen of the hen. The semen-containing instrument is placed 2–4 cm into the vaginal orifice. As the semen is being deposited, the pressure applied to the hen’s abdomen is being released simultaneously. [8] The individual performing this procedure typically uses one hand to move and direct the tail feathers, while using the other hand to insert the instrument and semen into the vagina. [11]

General biology

Modern commercial broilers, for example, Cornish crosses and Cornish-Rocks[ citation needed ], are artificially selected and bred for large-scale, efficient meat production. They are noted for having very fast growth rates, a high feed conversion ratio, and low levels of activity. Modern commercial broilers are bred to reach a slaughter-weight of about 2 kg in only 35 to 49 days. [5] [12] [13] As a consequence, the behaviour and physiology of broilers reared for meat are those of immature birds, rather than adults. Slow growing free-range and organic strains have been developed which reach slaughter-weight at 12 to 16 weeks of age.

Typical broilers have white feathers and yellowish skin. Recent genetic analysis has revealed that the gene for yellow skin was incorporated into domestic birds through hybridization with the grey junglefowl (G. sonneratii). [14] Modern crosses are also favorable for meat production because they lack the typical "hair" which many breeds have that must be removed by singeing after plucking the carcass.

Both male and female broilers are reared for their meat.


Broiler behaviour is modified by the environment, and alters as the broilers’ age and bodyweight rapidly increase. For example, the activity of broilers reared outdoors is initially greater than broilers reared indoors, but from six weeks of age, decreases to comparable levels in all groups. [15] The same study shows that in the outdoors group, surprisingly little use is made of the extra space and facilities such as perches – it was proposed that the main reason for this was leg weakness as 80 per cent of the birds had a detectable gait abnormality at seven weeks of age. There is no evidence of reduced motivation to extend the behavioural repertoire, as, for example, ground pecking remained at significantly higher levels in the outdoor groups because this behaviour could also be performed from a lying posture rather than standing.

Examining the frequency of all sexual behaviour shows a large decrease with age, suggestive of a decline in libido. The decline in libido is not enough to account for reduced fertility in heavy cocks at 58 weeks and is probably a consequence of the large bulk or the conformation of the males at this age interfering in some way with the transfer of semen during copulations which otherwise look normal. [16]

Feeding and feed conversion

Chickens are omnivores and modern broilers are given access to a special diet of high protein feed, usually delivered via an automated feeding system. This is combined with artificial lighting conditions to stimulate eating and growth and thus the desired body weight.

In the U.S. in 2011, the average feed conversion ratio of a broiler was 1.91 pounds of feed per pound of liveweight. In 1925 the figure was 4.70. [17]

Canada has a typical FCR of 1.72. [18]

New Zealand commercial broiler farms have recorded the world's best broiler chicken FCR, consistently at 1.38 or lower. [19]

Welfare issues

Meat birds

One-day old chicks arriving to be unpacked and placed in shed. Broiler chicks.jpg
One-day old chicks arriving to be unpacked and placed in shed.
Young birds being reared in a closed broiler house. Ayam.jpg
Young birds being reared in a closed broiler house.

Artificial selection has led to a great increase in the speed with which broilers develop and reach slaughter-weight. The time required to reach 1.5 kg live-weight decreased from 120 days to 30 days between 1925 and 2005. Selection for fast early growth-rate, and feeding and management procedures to support such growth, have led to various welfare problems in modern broiler strains. [20] Welfare of broilers is of particular concern given the large number of individuals that are produced; for example, the U.S. in 2011 produced approximately 9 billion broiler chickens. [21]

Cardiovascular dysfunction

Selection and husbandry for very fast growth means there is a genetically induced mismatch between the energy-supplying organs of the broiler and its energy-consuming organs. [13] Rapid growth can lead to metabolic disorders such as sudden death syndrome (SDS) and ascites. [20]

SDS is an acute heart failure disease that affects mainly male fast-growing broilers which appear to be in good condition. Affected birds suddenly start to flap their wings, lose their balance, sometimes cry out and then fall on their backs or sides and die, usually all within a minute. In 1993, U.K. broiler producers reported an incidence of 0.8%. In 2000, SDS has a death rate of 0.1% to 3% in Europe. [13]

Ascites is characterised by hypertrophy and dilatation of the heart, changes in liver function, pulmonary insufficiency, hypoxaemia and accumulation of large amounts of fluid in the abdominal cavity. Ascites develops gradually and the birds suffer for an extended period before they die. In the UK, up to 19 million broilers die in their sheds from heart failure each year. [22]

Skeletal dysfunction

Breeding for increased breast muscle means that the broilers’ centre of gravity has moved forward and their breasts are broader compared with their ancestors, which affects the way they walk and puts additional stresses on their hips and legs. [13] There is a high frequency of skeletal problems in broilers, mainly in the locomotory system, including varus and valgus deformities, osteodystrophy, dyschondroplasia and femoral head necrosis. [20] These leg abnormalities impair the locomotor abilities of the birds, and lame birds spend more time lying and sleeping. [23] The behavioural activities of broilers decrease rapidly from 14 days of age onwards. [24] Reduced locomotion also decreases ossification of the bones and results in skeletal abnormalities; these are reduced when broilers have been exercised under experimental conditions. [20]

Most broilers find walking painful, as indicated by studies using analgesic and anti-inflammatory drugs. In one experiment, healthy birds took 11 seconds to negotiate an obstacle course, whereas lame birds took 34 seconds. After the birds had been treated with carprofen, there was no effect on the speed of the healthy birds, however, the lame birds now took only 18 seconds to negotiate the course, indicating that the pain of lameness is relieved by the drug. [25] In self-selection experiments, lame birds select more drugged feed than non-lame birds [26] leading to the suggestion that leg problems in broilers are painful.

Several research groups have developed "gait scores" (GS) to objectively rank the walking ability and lameness of broilers. In one example of these scales, GS=0 indicates normal walking ability, GS=3 indicates an obvious gait abnormality which affects the bird’s ability to move about and GS=5 indicates a bird that cannot walk at all. GS=5 birds tried to use their wings to help them walking, or crawled along on their shanks. In one study, almost 26% of the birds examined were rated as GS=3 or above and can therefore be considered to have suffered from painful lameness. [13]

Compassion in World Farming wrote on the incidence of leg problems in broilers:

The video recordings below are examples of broilers attempting to walk with increasing levels of gait abnormalities and therefore increasing gait scores.

Integument lesions

Sitting and lying behaviours in fast growing strains increase with age from 75% in the first seven days to 90% at 35 days of age. This increased inactivity is linked with an increase in dermatitis caused by a greater amount of time in contact with ammonia in the litter. This contact dermatitis is characterised by hyperkeratosis and necrosis of the epidermis at the affected sites; it can take forms such as hock burns, breast blisters and foot pad lesions. [20]

Stocking density

Broilers in a rearing shed indicating the high stocking densities used. Ptichnik.JPG
Broilers in a rearing shed indicating the high stocking densities used.

Broilers are usually kept at high stocking densities which vary considerably between countries. Typical stocking densities in Europe range between about 22 to 42 kg/m2 or between about 11 to 25 birds per square metre. [13] There is a reduction of feed intake and reduced growth rate when stocking density exceeds approximately 30 kg/m2 under deep litter conditions. The reduced growth rate is likely due to a reduced capacity to lose heat generated by metabolism. Higher stocking densities are associated with increased dermatitis including food pad lesions, breast blisters and soiled plumage. [20] In a large-scale experiment with commercial farms, it was shown that the management conditions (litter quality, temperature and humidity) were more important than stocking density. [27]

Ocular dysfunction

In attempts to improve or maintain fast growth, broilers are kept under a range of lighting conditions. These include continuous light (fluorescent and incandescent), continuous darkness, or under dim light; chickens kept under these light conditions develop eye abnormalities such as macrophthalmos, avian glaucoma, ocular enlargement and shallow anterior chambers. [28] [29]


The litter in broiler pens can become highly polluted from the nitrogenous feces of the birds and produce ammonia. Ammonia has been shown to cause increased susceptibility to disease and other health-related problems such as Newcastle disease, airsaculitis and keratoconjunctivitis. The respiratory epithelium in birds is damaged by ammonia concentrations in the air exceeding 75 parts per million (ppm). Ammonia concentrations at 25 to 50 ppm induce eye lesions in broiler chicks after seven days of exposure. [29]

Catching and transport

Once the broilers have reached the target live-weight, they are caught, usually by hand, and packed live into crates for transport to the slaughterhouse. They are usually deprived of food and water for several hours before catching until slaughter. The process of catching, loading, transport and unloading causes serious stress, injury and even death to a large number of broilers.

The number of broilers that died in the EU in 2005 during the process of catching, packing and transport was estimated to be as high as 18 to 35 million. In the UK, of broilers that were found to be ‘dead on arrival’ at the slaughterhouse in 2005, it was estimated that up to 40% may have died from thermal stress or suffocation due to crowding on the transporter. [13]

Slaughter is done by hanging the birds fully conscious by their feet upside-down in shackles on a moving chain, stunning them by automatically immersing them in an electrified water bath and exsanguination by cutting their throats.

Some research indicates that chickens might be more intelligent than previously supposed, which "raises questions about how they are treated". A possible 10-year life span has been shortened to six weeks for broilers. [30]

Mortality rates

According to historical records, broiler mortality rates are decreasing. In 1925, the mortality rate in the U.S. was 18% compared to 3.8% in 2011. [17]

One indication of the effect of broilers' rapid growth rate on welfare is a comparison of the usual mortality rate for standard broiler chickens (1% per week) with that for slower-growing broiler chickens (0.25% per week) and with young laying hens (0.14% per week); the mortality rate of the fast-growing broilers is seven times the rate of laying hens (the same subspecies) of the same age. [13]

Parent birds

Meat broilers are usually slaughtered at approximately 35 to 49 days of age, well before they become sexually reproductive at 5 to 6 months of age. However, the bird's parents, often called "broiler-breeders", must live to maturity and beyond so they can be used for breeding. As a consequence, they have additional welfare concerns.

Meat broilers have been artificially selected for an extremely high feeding motivation, but are not usually feed-restricted, as this would delay the time taken for them to reach slaughter-weight. Broiler-breeders have the same highly increased feeding motivation, but must be feed-restricted to prevent them becoming overweight with all its concomitant life-threatening problems. An experiment on broilers’ food intake found that 20% of birds allowed to eat as much as they wanted either died or had to be killed because of severe illness between 11 and 20 weeks of age – either they became so lame they could not stand or they developed cardiovascular problems. [13]

Broiler breeders fed on commercial rations eat only a quarter to a half as much as they would with free access to food. They are highly motivated to eat at all times, presumably leading to chronic frustration of feeding. [31]

Because broiler breeders live to adulthood, they might show feather pecking or other injurious pecking behaviour. To avoid this, they might be beak trimmed which can lead to acute or chronic pain.

World production and consumption

Estimated chicken consumption per person in 2012. Meat Atlas 2014 Estimated chicken consumption.png
Estimated chicken consumption per person in 2012.

A report in 2005 stated that around 5.9 billion broiler chickens for eating were produced yearly in the European Union. Mass production of chicken meat is a global industry and at that time, only two or three breeding companies supplied around 90% of the world’s breeder-broilers. The total number of meat chickens produced in the world was nearly 47 billion in 2004; of these, approximately 19% were produced in the US, 15% in China, 13% in the EU25 and 11% in Brazil. [13]

Consumption of broilers is surpassing that of beef in industrialized countries. Demand in Asia is rising. [32]

Worldwide, 86.6 million tonnes of broiler meat were produced in 2014. [33]

As of 2018, the worldwide estimation of broiler chick population is approximately 23 billion. [34]

Broiler industry

The commercial production of broiler chickens for meat consumption is a highly industrialized process. There are two major sectors: (1) rearing birds intended for consumption and (2) rearing parent stock for breeding the meat birds.

See also

Related Research Articles

Poultry category of domesticated birds

Poultry are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes.

Debeaking the trimming of a birds beak, usually performed on domesticated birds like chickens

Debeaking is the partial removal of the beak of poultry, especially layer hens and turkeys although it may also be performed on quail and ducks. Most commonly, the beak is shortened permanently, although regrowth can occur. The trimmed lower beak is somewhat longer than the upper beak.

Animal husbandry Management, selective breeding, and care of farm animals by humans

Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, eggs, or other products. It includes day-to-day care, selective breeding and the raising of livestock.

Domestic turkey bird grown for Xmas dinners

The domestic turkey is a large fowl, one of the two species in the genus Meleagris and the same as the wild turkey. Although turkey domestication was thought to have occurred in central Mesoamerica at least 2,000 years ago, recent research suggests a possible second domestication event in the Southwestern United States between 200 BC and AD 500. However, all of the main domestic turkey varieties today descend from the turkey raised in central Mexico that was subsequently imported into Europe by the Spanish in the 16th century.

Pastured poultry

Pastured poultry is a sustainable agriculture technique that calls for the raising of laying chickens, meat chickens (broilers), and/or turkeys on pasture, as opposed to indoor confinement. Humane treatment and the perceived health benefits of pastured poultry are causing an increase in demand for such products.

Free range

Free range denotes a method of farming husbandry where the animals, for at least part of the day, can roam freely outdoors, rather than being confined in an enclosure for 24 hours each day. On many farms, the outdoors ranging area is fenced, thereby technically making this an enclosure, however, free range systems usually offer the opportunity for the extensive locomotion and sunlight that is otherwise prevented by indoor housing systems. Free range may apply to meat, eggs or dairy farming.

Tibial dyschondroplasia (TD) is a metabolic disease of young poultry that affects the growth of bone and cartilage. Often occurs in broilers and other poultry which have been bred for fast growth rates. The tibial cartilage does not mature enough to ossify. This leaves the growth plate prone to fracture, infection, and deformed bone development. It is the leading cause of lameness, mortality, and carcass condemnations in commercial poultry.

Forced molting

Forced molting, sometimes known as induced molting, is the practice by some poultry industries of artificially provoking a flock to molt simultaneously, typically by withdrawing food for 7–14 days and sometimes also withdrawing water for an extended period. Forced molting is usually implemented when egg-production is naturally decreasing toward the end of the first egg-laying phase. During the forced molt, the birds cease producing eggs for at least two weeks, which allows the bird's reproductive tracts to regress and rejuvenate. After the molt, the hen's egg production rate usually peaks slightly lower than the previous peak, but egg quality is improved. The purpose of forced molting is therefore to increase egg production, egg quality, and profitability of flocks in their second or subsequent laying phases, by not allowing the hen's body the necessary time to rejuvenate during the natural cycle of feather replenishment.

Chick culling is the process of killing newly hatched poultry for which the industry has no use. It occurs in all industrialised egg production whether free range, organic, or battery cage—including that of the UK and US. Because male chickens do not lay eggs and only those on breeding programmes are required to fertilise eggs, they are considered redundant to the egg-laying industries and are usually killed shortly after being sexed, which occurs after they hatch. Many methods of culling do not involve anaesthetics and include cervical dislocation, asphyxiation by carbon dioxide and maceration using a high speed grinder. Asphyxiation is the primary method in the United Kingdom, while maceration is the primary method in the United States. By 2020, US producers expect to sex the eggs before they hatch, so male eggs can be culled.

Hock burns are marks found on the upper joints of chickens and other birds raised on broiler farms. These marks are where the ammonia from the waste of other birds has burned through the skin of the leg, leaving a mark. Many meat processors now remove these marks as they discourage customers. Hock burn normally does not surpass 15% of a flock, according to poultry industry standards, but independent studies have found incidents of hock burn more common. Researchers in Britain found that hock burn could be identified in 82% of chickens sold in supermarkets.

Intensive animal farming

Intensive animal farming or industrial livestock production, also known as factory farming, is a production approach towards farm animals in order to maximize production output, while minimizing production costs. Intensive farming refers to animal husbandry, the keeping of livestock such as cattle, poultry, and fish at higher stocking densities than is usually the case with other forms of animal agriculture—a practice typical in industrial farming by agribusinesses. The main products of this industry are meat, milk and eggs for human consumption. There are issues regarding whether factory farming is sustainable or ethical.

Poultry farming Part of animal husbandry

Poultry farming is the process of raising domesticated birds such as chickens, ducks, turkeys and geese for the purpose of farming meat or eggs for food. Poultry – mostly chickens – are farmed in great numbers. Farmers raise more than 50 billion chickens annually as a source of food, both for their meat and for their eggs. Chickens raised for eggs are usually called layers while chickens raised for meat are often called broilers.

Chelates in animal nutrition

Chelates [kee-leyt] in animal feed are organic forms of essential trace minerals such as copper, iron, manganese and zinc.

Pale, Soft, Exudative meat, or PSE meat, describes a carcass quality condition known to occur in pork, beef, and poultry. It is characterized by an abnormal color, consistency, and water holding capacity, making the meat dry and unattractive to consumers. The condition is believed to be caused by abnormal muscle metabolism following slaughter, due to an altered rate of glycolysis and a low pH within the muscle fibers. A mutation point in the ryanodine receptor gene (RYR1) in pork, associated to stress levels prior to slaughter are known to increase the incidence of PSE meat. Although the term "soft" may look positive, it refers to raw meat. When cooked, there is higher cook loss and the final product is hard, not juicy.

Naked Neck chicken breed

The Naked Neck is a breed of chicken that is naturally devoid of feathers on its neck and vent. The breed is also called the Transylvanian Naked Neck, as well as the Turken. Originally from Transylvania and was largely developed in Germany. The name "Turken" arose from the mistaken idea that the bird was a hybrid of a chicken and the domestic turkey. Naked Necks are fairly common in Europe today, but are rare in North America and very common in South America. The trait for a naked neck is a dominant one controlled by one gene and is fairly easy to introduce into other breeds, however these are hybrids rather than true Naked Necks, which is a breed recognized by the American Poultry Association since 1965, it was introduced in Britain in the 1920s. There are other breeds of naked necked chicken, such as the French naked neck, which is often confused with the Transylvanian, and the naked necked gamefowl.

Heritage turkey

A heritage turkey is one of a variety of strains of domestic turkey which retains historic characteristics that are no longer present in the majority of turkeys raised for consumption since the mid-20th century. Heritage turkeys can be differentiated from other domestic turkeys in that they are biologically capable of being raised in a manner that more closely matches the natural behavior and life cycle of wild turkeys. Heritage turkeys have a relatively long lifespan and a much slower growth rate than turkeys bred for industrial agriculture, and unlike industrially-bred turkeys, can reproduce without artificial insemination.

Poultry farming in the United States part of the United Statess agricultural economy

Poultry farming is a part of the United States's agricultural economy.

Dwarfism in chickens

Dwarfism in chickens is an inherited condition found in chickens consisting of a significant delayed growth, resulting in adult individuals with a distinctive small size in comparison with normal specimens of the same breed or population.

Broiler industry

The broiler industry is the process by which broiler chickens are reared and prepared for meat consumption.

Ugachick Limited, whose complete name is Ugachick Poultry Breeders Uganda Limited, but is commonly referred to as Ugachick, is a poultry breeding and marketing company in Uganda.


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