Motivational basis
Poultry species which exhibit cannibalism areCauses
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.Crowd size
Poultry have a social hierarchy. When crowds are too close together, dominant birds will fight more often to obtain or sustain dominance which can increase risk of cannibalism. 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. 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. 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.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 (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. This is due to the social order created by poultry, as well as their attraction to blood. 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. 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. 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,Hill, J.A. (1986). Egg production in alternative systems - a review of recent research in the UK. Research and Development in Agriculture, 3: 13-18 straw yards,Gibson, S.W., Dun, P. and Hughes, B.O., (1988). The performance and behaviour of laying fowls in a covered strawyard system. Research and Development in Agriculture, 5: 153-163 and free-range systems.Keeling, L.J., Hughes, B.O. and Dun, P., (1988). Performance of free range laying hens in a polythene house and their behaviour on range. Farm Building Progress, 94: 21-28 Because egg-laying strains of chickens can be kept in smaller group sizes in cage systems, cannibalism is reduced,Appleby, M.C. and Hughes, B.O., (1991). Welfare of laying hens in cages and alternative systems: Environmental, physical and behavioural aspects. World's Poultry Science Journal, 47:109-128 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.Sherwin, C.M., Richards, G.J. and Nicol, C.J., (2010). Comparison of the welfare of layer hens in 4 housing systems in the UK. British Poultry Science, 51: 488-499Methods 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.Flock, D.K., Laughlin K.F. and Bentley, J., (2005). Minimizing losses in poultry breeding and production: how breeding companies contribute to poultry welfare. World's Poultry Science Journal, 61: 227–237 This method can be considered cruel as it causes acute and chronic pain to the bird. 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.Lay Jr., D.C., Fulton, R.M., Hester, P.Y., Karcher, D.M., Kjaer, J.B., Mench, J.A., Mullens, B.A., Newberry, R.C., C.J., O'Sullivan, N.P. and Porter, R.E., (2011). Hen welfare in different housing systems. Poultry Science, 90: 278-294Light manipulations
Lights are sometimes provided in nest-boxes to attract hens to use the nests. However, this practice has been correlated with an increased risk of cannibalism.Zimmerman, P.H., Lindberg, A.C., Pope, S.J., Glen, E., Bolhuis, J.E. and Nicol, C.J., (2006). The effect of stocking density, flock size and modified management on laying hen behaviour and welfare in a non-cage system. Applied Animal Behaviour Science, 101: 111–124Perches
Rearing chicks with access to perches by four weeks of age has been associated with increased use of perches, and reduced cannibalism, in adulthood.Gunnarsson, S., Keeling, L.J. and Svedberg, J., (1999). Effects of rearing factors on the prevalence of floor eggs, cloacal cannibalism and feather pecking in commercial flocks of loose housed laying hens. British Poultry Science, 40: 12–18Selective 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.Nordquist, R.E., Heerkens, J.L.T., Rodenburg, T.B., Boks, S., Ellen, E.D. and van der Staay, F.J., (2011). Laying hens selected for low mortality: Behaviour in tests of fearfulness, anxiety and cognition. Applied Animal Behaviour Science, 131: 110-122Eyewear
Cannibalism may be reduced by fitting hens with a range of eyewear. Rose-tintedNature 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 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. Another study found that brown-egg laying hens are more likely to engage in feather pecking than white-egg laying hens. 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. 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. 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
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. 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. 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. 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. 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, it is ultimately 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. 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. To minimize cannibalism in domesticated poultry, different approaches such as ecology, environmental physiology, epidemiology, molecular genetics and ethology have been taken. However, the approach with the most success was the molecular genetic with behavioural research. This could lead to the decline of server practices to reduce cannibalism such as beak trimming.See also
* Animal cannibalism * Abnormal behaviour of birds in captivity * Battery cages *References
{{Cannibalism Abnormal behaviour in animals