Hock burns are lesions found on the hock joints of chickens and other birds raised on broiler farms. They are considered a form of contact dermatitis. [1] These marks occur when the ammonia from the waste of other birds burns through the skin of the leg, leaving a brown ulcer mark. [2] The condition has been found to be a source of pain for birds, can cause mobility issues, and may increase the risk of bacterial diseases. [3] [4] [5] In severe cases, hock burns can cause visible scabs to form. [6]
Higher rates of hock burns are often used by observers as an indicator of what they see as worse animal welfare conditions. [5] This is in part due to how they occur more often in overcrowded conditions and in birds genetically modified to grow fast. Although the meat is still safe to eat, many processors now remove these marks as they discourage customers. [2]
Hock burns have been identified in birds in Northern Ireland since at least 1978. It appears to have been first described in the scientific literature in a brief account in 1983. [7] From 1984 to 1987, hock burns were identified in 21% of birds. [8] In the decades since its first identification, it has stayed at an overall increased level. [9]
The industry standard target is to have no more than 15% of a flock showing hock burns, but independent studies have found that incidents are more common. [10] In 2024, self-reported data suggests a prevalence of around one-third of farmed birds in the United Kingdom. Spot checks of stores by volunteers found higher rates of 74% for one store's supplier. [2] Researchers in 2005 doing store spot checks found similar rates of around 80% across the United Kingdom. The same researchers also discovered a potential methodological difference between spot check figures and other reported values. After talking with veterinary inspectors, they were told that some slaughterhouses only record large hock burns and do not pay attention to anything smaller. [11]
Hock burns are not limited to the United Kingdom. For instance, in Brazil, hock burns are one of the most frequent causes of carcass condemnation (inspector rejection of meat). [12] In Germany, one study found that over a third of conventional broilers had hock burns. [13]
Various animal rights and animal welfare groups have criticized the prevalence of hock burns. For instance, one poultry specialist at the RSPCA has called it concerning and "sadly too common" in intensive animal farming. Other groups, such as Open Cages, have called it a sign of larger issues within the industry. [2]
A number of factors are known to contribute to higher rates of hock burns. These include using fast-growing birds, higher stocking densities, and high moisture levels in the litter where birds live. [14] [15] Additionally, it has been found to be more common in male birds and more common in heavier birds. [16] Research suggests that many of the same factors also contribute to foot pad dermatitis, another similar condition. Hock burn and foot pad dermatitis are often found together in the same birds. [14]
While there is not a fully universal way to classify the severity of hock burn, several methods exist. The most common relies on visual data and is called the Welfare Quality Assessment Protocol. [17] This method puts cases on a five-point scale from zero to four, with zero being no evidence of hock burns and four showing the most severe lesions. [18] Another alternative method works similarly, but rates cases on a three-point scale. [19]
Poultry are domesticated birds kept by humans for the purpose of harvesting animal products such as meat, eggs or feathers. The practice of raising poultry is known as poultry farming. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes. The term also includes waterfowls of the family Anatidae but does not include wild birds hunted for food known as game or quarry.
Breed broiler is any chicken that is bred and raised specifically for meat production. Most commercial broilers reach slaughter weight between four and six weeks of age, although slower growing breeds reach slaughter weight at approximately 14 weeks of age. Typical broilers have white feathers and yellowish skin. Broiler or sometimes broiler-fryer is also used sometimes to refer specifically to younger chickens under 2.0 kilograms, as compared with the larger roasters.
Poultry diseases occur in poultry, which are domesticated birds kept for their meat, eggs or feathers. Poultry species include the chicken, turkey, duck, goose and ostrich.
Avian coronavirus is a species of virus from the genus Gammacoronavirus that infects birds; since 2018, all gammacoronaviruses which infect birds have been classified as this single species. The strain of avian coronavirus previously known as infectious bronchitis virus (IBV) is the only coronavirus that infects chickens. It causes avian infectious bronchitis, a highly infectious disease that affects the respiratory tract, gut, kidney and reproductive system. IBV affects the performance of both meat-producing and egg-producing chickens and is responsible for substantial economic loss within the poultry industry. The strain of avian coronavirus previously classified as Turkey coronavirus causes gastrointestinal disease in turkeys.
Histomonas meleagridis is a species of parasitic protozoan that infects a wide range of birds including chickens, turkeys, peafowl, quail and pheasants, causing infectious enterohepatitis, or histomoniasis. H. meleagridis can infect many birds, but it is most deadly in turkeys. It inhabits the lumen of cecum and parenchyma of liver, where it causes extensive necrosis. It is transmitted by another cecal parasite, the nematode Heterakis gallinarum.
Dermanyssus gallinae is a haematophagous ectoparasite of poultry. It has been implicated as a vector of several major pathogenic diseases. Despite its common names, it has a wide range of hosts including several species of wild birds and mammals, including humans, where the condition it causes is called gamasoidosis. In both size and appearance, it resembles the northern fowl mite, Ornithonyssus sylviarum.
Poultry farming is the form of animal husbandry which raises domesticated birds such as chickens, ducks, turkeys and geese to produce meat or eggs for food. Poultry – mostly chickens – are farmed in great numbers. More than 60 billion chickens are killed for consumption annually. Chickens raised for eggs are known as layers, while chickens raised for meat are called broilers.
Histomoniasis is a commercially significant disease of poultry, particularly of chickens and turkeys, due to parasitic infection of a protozoan, Histomonas meleagridis. The protozoan is transmitted to the bird by the nematode parasite Heterakis gallinarum. H. meleagridis resides within the eggs of H. gallinarum, so birds ingest the parasites along with contaminated soil or food. Earthworms can also act as a paratenic host.
Avian orthoreovirus, also known as avian reovirus, is an orthoreovirus from the Reoviridae family. Infection causes arthritis and tenosynovitis in poultry. It can also cause respiratory disease.
Pacheco's disease is a highly infectious and acute bird disease caused by a species of herpesvirus, Psittacid alphaherpesvirus 1 (PsHV-1). All psittacine species are susceptible to Pacheco's disease, mainly those in zoological collections and aviaries in any geographic regions. Pacheco's disease most commonly occurs in Amazon parrots, followed by African grey parrots, parrots, macaws, cockatoos and conures. Due to a very high mortality rate within these susceptible species, concerns are brought to companion bird markets and breeders.
Raillietina cesticillus is a parasitic tapeworm of the family Davaineidae. Sometimes called "Broad-headed tapeworm", it infects the small intestine of chicken and occasionally other birds, such as guinea fowl and turkey, which are generally in close proximity to backyard poultry. It is a relatively harmless species among intestinal cestodes in spite of a high prevalence. In fact it probably is the most common parasitic platyhelminth in modern poultry facilities throughout the world.
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.
Egg drop syndrome '76 is a viral disease that affects birds, notably chickens, ducks, geese and swans. It is characterised by a sudden drop in production of eggs as well as its eggshell quality in apparent healthy laying birds.
Avibirnavirus is a genus of viruses in family Birnaviridae. There is a single species in this genus: Infectious bursal disease virus, which infects chickens and other fowl. It causes severe inflammation of the bursa of Fabricius, and causes considerable morbidity and mortality.
Clostridium colinum is a Gram-positive, anaerobic and spore-forming bacterium from the genus Clostridium which has been isolated from a chicken. Clostridium colinum can cause ulcerative enteritis in chicken.
Influenza A virus subtype H10N3 is a subtype of viruses that causes influenza (flu). It is mostly present in wild avian species. The first human case was reported in 2021.
Airsacculitis, also known as air sacculitis, aerosacculitis, air sac disease, air sac infection, air sac syndrome and simply sac disease, is a common inflammatory condition of air sacs that occurs in birds and is caused by various microbial taxa. Having multiple different causative agents, the condition is widely distributed around the world.
The poultry microbiome is an understudied, yet extremely impactful part of the poultry industry. Poultry is defined as any avian species used for production purposes such as food or down feathers. The United States consumes more poultry, specifically broiler meat, than any other type of protein. Worldwide, poultry makes up 33% of consumed meat. This makes poultry extremely valuable and the impact of the poultry microbiome on health and production even more valuable. Antonie van Leeuwenhoek was the first to notice microbes inside animals through stool samples giving light to further research into the gut microbiome. His discovery lead to the ever evolving study of the microbiota and microbiome. The microbiota is the entirety of living organisms including bacteria, viruses, fungi, and archaea in an environment. The microbiome is the combination of the microbiota and the additional activities in that system including metabolites and chemicals in a habitat. Much of the work done to characterize the poultry microbiome has been accomplished over the past decade and was done through the use of 16s rRNA sequencing.
The breeding and raising of broiler chickens has created health and animal welfare issues, such as cardiovascular and skeletal dysfunction.
White striping is a condition in poultry where white fat deposits replace muscle in stripes along muscle fibers. It is considered a type of myopathy, primarily of the Pectoralis major muscle. There does not appear to be direct harm to birds specifically from white striping. However, some scientists and animal welfare groups have called its presence indicative of the industry's use of fast-growing birds, who have higher rates of health issues and welfare concerns such as hock burns. Using fast-growing birds is linked to overall higher rates of white striping.