Cannibalism in poultry

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Image of domesticated poultry

Cannibalism in poultry is the act of one individual of a poultry species consuming all or part of another individual of the same species as food. It commonly occurs in flocks of domestic hens reared for egg production, although it can also occur in domestic turkeys, pheasants and other poultry species. [1] Poultry create a social order of dominance known as pecking order. [1] When pressure occurs within the flock, pecking can increase in aggression and escalate to cannibalism. [2] Cannibalism can occur as a consequence of feather pecking which has caused denuded areas and bleeding on a bird's skin. [3] Cannibalism can cause large mortality rates within the flock and large decreases in production due to the stress it causes. Vent pecking, sometimes called 'cloacal cannibalism', is considered to be a separate form of cannibalistic pecking as this occurs in well-feathered birds and only the cloaca is targeted. [4] [5] There are several causes that can lead to cannibalism such as: light and overheating, crowd size, nutrition, injury/death, genetics and learned behaviour. [6] [1] [2] Research has been conducted to attempt to understand why poultry engage in this behaviour, as it is not totally understood. There are known methods of control to reduce cannibalism such as crowd size control, beak trimming, light manipulation, perches, selective genetics and eyewear.

Contents

Motivational basis

Poultry species which exhibit cannibalism are omnivores. For example, hens in the wild often scratch at the soil to search for seeds, insects and even larger animals such as lizards or young mice, [7] although they are mainly herbivorous in adulthood. [3] Feather pecking is often the initial cause of an injury which then attracts the cannibalistic pecking of other birds – perhaps as re-directed foraging or feeding behaviour. In the close confines of modern farming systems, the increased pecking attention is easily observed by multiple birds which join in the attack, and often the escape attempts of the cannibalised bird attract more pecking attention.

Causes

Light and overheating

High intensity light with prolonged exposure can lead to cannibalism of poultry in captivity due to the increase of stress and overheating that causes discomfort. [1]

Crowd size

Poultry have a social hierarchy and when crowds are too close together, dominant birds will fight more often to obtain or sustain dominance which can increase risk of cannibalism. [1] [2] The increase crowd size also plays into a few more factors. With a larger crowd there is less space in the pen. This allows for less feeding space which therefore means that dominant birds will take majority of the food supply leaving less dominant birds susceptible to becoming underweight and easier targets to the dominant birds for cannibalism. [1] An optimal flock size are either large flock of greater than 30 where the group is too large to recognize an established dominant bird and the social hierarchy breaks down, or a small group size where a social order can easily organize itself. [1] Intermediate group sizes cause confusion among the flock and leads to higher aggression of different birds attempting to become the dominant one and therefore leading to increased risk of cannibalism. [1]

Nutrition

A particular diet of low protein but high energy is shown to lead to less aggressive behaviours, but despite that, a diet lacking the protein component (amino acid) methionine is shown to cause aggressive behaviours. [1] Methionine is an essential amino acid. [1] This means the body cannot produce the amino acid and needs an external source to obtain its required amount. Oftentimes in flocks it is the first limiting amino acids. [8] Methionine contains sulfur which is used to grow feathers and this may explain the biological purpose for increased pecking. [8] This pecking behavior then escalates into more extreme forms of cannibalism.

Poultry have a gland called the preen gland that secretes an oily, salty tasting substance. When their diets lack salt, the gland produces the oily substances but without the salty taste. The bird then believes it is not getting its requirement from the gland and will peck at other birds preen gland to meet their requirements. When the behaviour of pecking other birds is introduced, it can lead to increased risk of cannibalism. [1]

When feeding, it is important to give enough space and to lay the feed to mimic the environmental conditions and spread the feed so poultry spend time pecking at the food and not each other. [1]

Feather eating is another potential cause to cannibalism. Feather eating is a behaviour similar to feather pecking where poultry will peck at other members of the flock to eat their feathers. [2] In a study of F2 cross of hens for aggressive pecking behaviour it was seen that feather eating during a chicks rearing stage of life meant it had a higher likelihood of feather pecking in the laying stage of its life. [2] One reason they believed why feather eating was prevalent, is that keratin from feathers was not a nutritional source per se, but could enhance the gut microbiome. [2]

Injury or death

Within a pen, if another bird is injured or dead, the sight of this can encourage other pen members to engage in cannibalistic behaviours. [1] [6] This is due to the social order created by poultry, as well as their attraction to blood. [1] Poultry are attracted to the colour red and the sight of blood can cause them to be attracted to the injured bird and peck at it more to increase their rank in the pecking order. [9] Sometimes this even leads to their death.

Prevalence

Cannibalism among layer hen flocks is highly variable; when it is not problematic, mortalities among production systems are generally similar. [10] Published data on the prevalence of cannibalism could be misleading due to the inclusion of vent-pecking by some researchers but not others. Mortalities, due mainly to cannibalism, can be up to 15% in egg-laying flocks housed in aviaries, [11] straw yards, [12] and free-range systems. [13] Because egg-laying strains of chickens can be kept in smaller group sizes in cage systems, cannibalism is reduced, [10] leading to a lowered trend in mortality as compared to non-cage systems. In a study which examined 'skin damage' (most of which would have been caused by pecking) on hens at the end of their productive lives, damage was lowest in hens from free range systems, followed by barns, then furnished cages, and highest in conventional or battery cages. [14]

Methods of control

Beak-trimming

Beak-trimming is the most common method of preventing or reducing injuries by cannibalism. In a three-year study of floor-housed laying hens, death by cannibalism was reported as 7% in beak-trimmed birds but was increased to 18% in non-trimmed birds. [15] This method can be considered cruel as it causes acute and chronic pain to the bird. [16] The beaks of poultry are highly sensitive to pain, touch, heat and pressure. They use their beaks to forage the ground. Trimming their beaks makes them lose their ability to sense the external world and could cause neuromas, which are bundles of severed nerve endings becoming exposed due to beak trimming.

Group size

Increased group sizes in larger cages or floor systems can elevate the risk of cannibalism and feather pecking, probably due to the spread of the behaviour through social learning. [17]

Light manipulations

Lights are sometimes provided in nest-boxes to attract hens to use the nests, but this practice has been correlated with an increased risk of cannibalism. [18]

Perches

Rearing chicks with access to perches by four weeks of age has been associated with increased use of perches, and reduced cannibalism, in adulthood. [19]

Selective breeding and genetics

A sibling-selection programme has genetically selected a low mortality line which shows decreased mortality from cannibalism compared to a control line. [20]

Eyewear

Cannibalism may be reduced by fitting hens with a range of eyewear. Rose-tinted glasses or contact lenses have been used. Opaque spectacles, or blinders, have also been used. For both spectacles and blinders, there are versions held in place by circlips in the nares of the bird, or others in which a pin pierces the nasal septum. The piercing method is illegal in the UK. [21] It is theorized that — as with placing red filters over windows, or keeping the birds in red light — the coloured lenses prevent the birds from recognising the blood or raw flesh of other hens, thereby diminishing cannibalistic behaviour. [22]

Nature vs. nurture

While cannibalism of poultry is a learned behaviour, there is a genetic component that can make the bird be more susceptible to engaging or initiating cannibalism.

Nature

Pecking and other forms of pecking (feather pecking, vent pecking, aggressive pecking) are normal behaviours that have genetic influences [1] [2] [6] One study in the Netherlands tested if a specific farming style had an effect on cannibalism. During the study they estimated the heredity of feather pecking to be as high as 0.56. [6] Another study found that brown-egg laying hens are more likely to engage in feather pecking than white-egg laying hens. [1] The genetics of poultry will not guarantee a bird will engage in cannibalism, but the genes a bird possesses play a part in the degree of aggressiveness a bird could engage in feather pecking and increases their risk engaging in cannibalism.

Certain genetic technologies such as linkage analysis could identify genes related to feather pecking and could be screened against to select birds that are less likely to engage in pecking. [6] However, one study found a correlation between feather pecking and egg production and found that birds that engage in high feather-pecking behaviour had on average had a higher egg production. [2] Therefore, selecting against feather pecking could reduce egg production. Farmers would have to choose between a trade off of either possibly having higher egg production with a high potential of flock death due to cannibalism, versus lower egg production with a lower risk of death due to cannibalism.

Nurture

As mentioned before, pecking and feather pecking are normal behaviours, but cannibalism can be learned. Feather eating is also a normal behaviour that can lead the bird into engaging in feather pecking. As a chick during rearing engages in feather eating, they are more likely to engage in feather pecking during the "laying" stage of their lives. [2] Furthermore, if a member of the flock has had its feather pecked, they will stay in this category as the damage to the feathers are a physical indicator to others that that bird is being targeted. [2] One study found that fear could increase feather pecking and primary cannibals can influence secondary cannibals by initiating cannibalism by becoming more aggressive in pecking. [2] Cannibalism within a flock is seen as a chain reaction where if one member of the flock begins, if left unattended, will cause others around it to learn the behaviour and engage in cannibalism. [6] The social order of a flock will also play into the risk of cannibalism. This can be seen if a primary cannibal is a higher ranked bird in the flock, it could influence more secondary cannibals and spread this behaviour more rapidly.

Genotype-environmental interaction

While genetics and learned experience can influence behaviour, ultimately it is an interaction of the two that gives the expressed behaviour. The Netherlands study found the flocks of the same breed had different outcomes of whether cannibalism developed or not depending on the management control of the different farms the flocks grew up in. [6] While the genetics of these flocks were similar, the environmental factors ultimately influences the introduction of cannibalism in the flocks. In some flocks 36.4% of the deaths due to cannibalism was observed. [6] To minimize cannibalism in domesticated poultry, different approaches such as ecology, environmental physiology, epidemiology, molecular genetics and ethology have been taken. But the approach with the most success was the molecular genetic with behavioural research and could lead to the decline of server practices to reduce cannibalism such as beak trimming.

See also

Related Research Articles

<span class="mw-page-title-main">Poultry</span> Domesticated birds kept by humans for their eggs, meat, or feathers

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.

<span class="mw-page-title-main">Chicken</span> Domesticated species of bird

The chicken is a large and round short-winged bird, domesticated from the red junglefowl of Southeast Asia around 8,000 years ago. Most chickens are raised for food, providing meat and eggs; others are kept as pets or for cockfighting.

<span class="mw-page-title-main">Debeaking</span> Trimming of a birds beak, usually performed on domesticated birds

Debeaking, beak trimming, or beak conditioning 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. A similar but separate practice, usually performed by an avian veterinarian or an experienced birdkeeper, involves clipping, filing or sanding the beaks of captive birds for health purposes – in order to correct or temporarily to alleviate overgrowths or deformities and better allow the bird to go about its normal feeding and preening activities. Amongst raptor-keepers, this practice is commonly known as "coping".

<span class="mw-page-title-main">Domestic turkey</span> Species of bird

The domestic turkey is a large fowl, one of the two species in the genus Meleagris and the same species 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 area that is now the southwestern United States between 200 BC and 500 AD. 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.

<span class="mw-page-title-main">Broiler</span> Chicken bred for meat

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.

<span class="mw-page-title-main">Free-range eggs</span> Type of egg produced from outdoor bird

Free-range eggs are eggs produced from birds that may be permitted outdoors. The term "free-range" may be used differently depending on the country and the relevant laws, and is not regulated in many areas.

<span class="mw-page-title-main">Free range</span> Method of farming where animals can roam freely outdoors

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.

<span class="mw-page-title-main">Forced molting</span> Practice of artificially provoking a flock to molt simultaneously

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.

<span class="mw-page-title-main">Battery cage</span> Agricultural technology

Battery cages are a housing system used for various animal production methods, but primarily for egg-laying hens. The name arises from the arrangement of rows and columns of identical cages connected, in a unit, as in an artillery battery. Although the term is usually applied to poultry farming, similar cage systems are used for other animals. Battery cages have generated controversy between advocates for animal welfare and industrial producers.

<span class="mw-page-title-main">Poultry farming</span> Part of animal husbandry

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.

<span class="mw-page-title-main">Dust bathing</span> Animal behavior

Dust bathing is an animal behavior characterized by rolling or moving around in dust, dry earth or sand, with the likely purpose of removing parasites from fur, feathers or skin. Dust bathing is a maintenance behavior performed by a wide range of mammalian and avian species. For some animals, dust baths are necessary to maintain healthy feathers, skin, or fur, similar to bathing in water or wallowing in mud. In some mammals, dust bathing may be a way of transmitting chemical signals to the ground which marks an individual's territory.

<span class="mw-page-title-main">Feather pecking</span> When one bird repeatedly pecks at the feathers of another

Feather pecking is a behavioural problem that occurs most frequently amongst domestic hens reared for egg production, although it does occur in other poultry such as pheasants, turkeys, ducks, broiler chickens and is sometimes seen in farmed ostriches. Feather pecking occurs when one bird repeatedly pecks at the feathers of another. The levels of severity may be recognized as mild and severe. Gentle feather pecking is considered to be a normal investigatory behaviour where the feathers of the recipient are hardly disturbed and therefore does not represent a problem. In severe feather pecking, however, the feathers of the recipient are grasped, pulled at and sometimes removed. This is painful for the receiving bird and can lead to trauma of the skin or bleeding, which in turn can lead to cannibalism and death.

<span class="mw-page-title-main">Abnormal behaviour of birds in captivity</span>

Abnormal behavior of birds in captivity has been found to occur among both domesticated and wild birds. Abnormal behavior can be defined in several ways. Statistically, 'abnormal' is when the occurrence, frequency or intensity of a behaviour varies statistically significantly, either more or less, from the normal value. This means that theoretically, almost any behaviour could become 'abnormal' in an individual. Less formally, 'abnormal' includes any activity judged to be outside the normal behaviour pattern for captive birds of that particular class or age. For example, running rather than flying may be a normal behaviour and regularly observed in one species, however, in another species it might be normal but becomes 'abnormal' if it reaches a high frequency, or in another species it is rarely observed and any incidence is considered 'abnormal'. This article does not include 'one-off' behaviours performed by individual birds that might be considered abnormal for that individual, unless these are performed repeatedly by other individuals in the species and are recognised as part of the ethogram of that species.

Vent pecking is an abnormal behaviour of birds performed primarily by commercial egg-laying hens. It is characterised by pecking damage to the cloaca, the surrounding skin and underlying tissue. Vent pecking frequently occurs immediately after an egg has been laid when the cloaca often remains partly everted exposing the mucosa, red from the physical trauma of oviposition or bleeding if the tissue is torn by her laying an egg. Vent pecking clearly causes pain and distress to the bird being pecked. Tearing of the skin increases susceptibility to disease and may lead to cannibalism, with possible evisceration of the pecked bird and ultimately, death.

Toe pecking, an abnormal behaviour of birds in captivity, occurs when one bird pecks the toes of another using its beak. This behaviour has been reported in hens and ostriches. Studies have shown that hens exposed to toe pecking have significantly enlarged adrenal glands, indicating increased physiological stress. Hens exposed to toe pecking will step off a raised platform more quickly than control hens, possibly suggesting a heightened fear of elevation. They have also been reported to show depressive behaviour when afflicted by toe-pecking. The act of toe pecking leads to open wounds which are viable for infection and disease to develop. In severe forms, toe pecking can be classified as a cannibalistic behaviour and has been reported as a cause of mortality.

<span class="mw-page-title-main">Furnished cage</span>

A furnished cage, sometimes called enriched cage, colony cage or modified cage, is a type of cage used in poultry farming for egg laying hens. Furnished cages have been designed to overcome some of the welfare concerns of battery cages whilst retaining their economic and husbandry advantages, and also provide some of the welfare advantages over non-cage systems. Many design features of furnished cages have been incorporated because research in animal welfare science has shown them to be of benefit to the hens.

<span class="mw-page-title-main">Chicken eyeglasses</span> Small eyeglasses made for chickens

Chicken eyeglasses, also known as chicken specs, chicken goggles, generically as pick guards, and under other names, were small eyeglasses made for chickens intended to prevent feather pecking and cannibalism. They differ from blinders in that they allow the bird to see forward, whereas blinders do not. One variety used rose-colored lenses, as the coloring was thought to prevent a chicken wearing them from recognizing blood on other chickens, which may increase the tendency for abnormal injurious behavior. They were mass-produced and sold throughout the United States as early as the beginning of the 20th century.

<span class="mw-page-title-main">Blinders (poultry)</span>

Blinders, also known as peepers, are devices fitted to, or through, the beaks of poultry to block their forward vision and assist in the control of feather pecking, cannibalism and sometimes egg-eating. A patent for the devices was filed as early as 1935. They are used primarily for game birds, pheasant and quail, but also for turkeys and laying hens. Blinders are opaque and prevent forward vision, unlike similar devices called spectacles which have transparent lenses. Blinders work by reducing the accuracy of pecking at the feathers or body of another bird, rather than spectacles which have coloured lenses and allow the bird to see forwards but alter the perceived colour, particularly of blood. Blinders are held in position with a circlip arrangement or lugs into the nares of the bird, or a pin which pierces through the nasal septum. They can be made of metal (aluminium), neoprene or plastic, and are often brightly coloured making it easy to identify birds which have lost the device. Some versions have a hole in the centre of each of the blinders, thereby allowing restricted forward vision.

<span class="mw-page-title-main">Pecking</span>

Pecking is the action of a bird using their beak to search for food or otherwise investigate an object or area by tapping it. Pecking can also be used by a bird to attack or fight another bird.

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