An Introduction to Cannibalism...

Cannibalistic behavior occurs throughout the animal kingdom in both wild and captive populations.  In the wild, cannibalism is perceived as an adaptive function that increases an individual’s fitness, by providing nutrients and simultaneously reducing competition for resources by eliminating competitors.  Within captive populations, however, cannibalism is perceived as an abnormal behavior and the mechanisms underlying its development are poorly understood.  In poultry, cannibalism involves beak inflicted injury followed by the consumption of blood and other tissues of conspecifics.  Evidence suggests that experiences early in life have important implications for the later development of cannibalism in poultry, and that cannibalistic behavior is a learned response that is enhanced by observing other birds engaging in the behavior.  

The Problems Revolving Around Cannibalism in Laying Hens...

Cannibalism constitutes a serious welfare and economic problem when live birds are injured or killed; and is, in fact, one of the main causes of mortality in laying hens.  The most common technique used to reduce cannibalistic behavior is beak trimming.  Beak trimming is a process whereby the tips of beaks are removed to prevent birds from being able to perform severe feather-pecking or cannibalism.  Despite it being common practice, beak trimming is not a suitable solution to the problem.  Behavioral and neurological evidence suggests that beak trimming causes both acute and chronic pain, leads to apathy, and has a negative effect on animal well-being.  There is a need for improvement in the strategies for alleviating cannibalistic behavior within the poultry industry; and it seems that a better understanding of the underlying processes of the behavior is necessary for the development of a more suitable solution to the problem.

What is the Driving Force Behind Cannibalistic Behavior in Laying Hens?

There are several hypotheses that attempt to explain the processes behind the development of cannibalism in laying hens.  The most compelling hypothesis, however, relates cannibalistic behavior to misdirected foraging behavior.  Several authors have stressed the close resemblance of feather pecking and cannibalism to foraging behavior.  The physical manipulations of the beak during bouts of cannibalistic behavior mirror the manipulations employed in foraging behavior.  Discussion into the similarities that link these behaviors has lead to the development of a foraging hypothesis for cannibalistic behavior.  Under the foraging hypothesis, feather pecking and cannibalism are thought to represent foraging behavior that becomes redirected towards conspecifics in the absence of more appropriate pecking stimuli.

What Factors Lead to the Misdirection of Foraging Behavior in Laying Hens?

It was once hypothesized that hens may choose to forage upon tissues of conspecifics to satisfy a need for additional protein within their diet.  The root of cannibalistic behavior would then be a protein deficiency.  The egg industry has become increasingly dependent on plant protein sources, in particular, soybean meal, as the main component of layer diets.  It has been suggested that the absence of animal protein in layer diets may be causally related to increased incidences of cannibalism.  Additionally, studies have looked at whether different levels of protein within the diet may influence cannibalistic behavior.  The evidence at hand, however, suggests that neither the form of protein nor the amount of protein provided in the diet have significant influence on the development or persistence of cannibalistic behavior within a flock.  Thus, it seems that the misdirection of foraging behavior toward conspecifics represents an inadequacy in the housing system, a deficiency of opportunity to forage, and not a deficiency in a nutritional aspect of foraging.

There is an apparent inverse relationship between cannibalism and foraging behavior.  It could be that this relationship occurs simply because if birds are engaged in foraging behavior for longer time spans, they have less time available for cannibalistic acts, and vise versa.    Evidence suggests that laying hen chicks housed on a litter floor (wood-shavings) exhibit more ground pecking and less feather pecking than chicks housed on slats.  In addition, if chicks are reared with access to novel materials that enhance foraging behavior, they exhibit fewer incidences of cannibalistic behavior later in life.  Inclusion of materials such as long-cut or bundled straw and sand as foraging materials within a housing system during rearing, leads to a significant decrease in the incidence of cannibalism within a flock.  Given the fact that a hen’s ability to manipulate foraging material changes during development, it may be necessary to provide diverse foraging material during different stages of the lifetime. 

Developing Strategies to Prevent or Reduce Cannibalism within a Flock
There is a need for innovative strategies in the attempt to reduce cannibalism among laying hens.  Introducing novel stimuli as appropriate foraging substrates is effective in reducing the incidence of cannibalism.  In practice, however, the cost of adding elements to a poultry housing system may cause farmers to avoid this strategy unless legislation mandates the process.  Therefore, it may be more practical to work with methods that alter elements already provided to the birds.

Several studies report that the risk of cannibalism is lower when hens are fed a mash diet (feed the consistency of “Grape Nuts”), which takes longer to eat, than when fed a diet consisting of pellets, which are quickly consumed.  An additional study found that hens fed food in ground form exhibited a significantly lower incidence of cannibalism, fewer skin lesions, and better feather condition than hens fed the same feed in pelleted form.  These findings support the idea that an increase in the time spent foraging reduces the incidence of cannibalism.  This has practical value, as poultry farmers could potentially reduce or prevent cannibalistic behavior among their flocks simply by increasing the time birds spend feeding.

The "Take Home" Message

Outbreaks of feather pecking and cannibalism in laying hens remain a serious problem in the egg industry, in terms of both welfare and economics.  In developing strategies to reduce cannibalism among laying hens, it is important to understand the causation of cannibalistic behavior.  An understanding of the underlying principles driving cannibalistic behavior will aid in the identification of housing and breeding conditions in which this behavior is reduced or does not develop.  Evidence suggests that cannibalistic behavior in laying hens is related to inadequate foraging substrate in current housing systems.  Therefore, providing proper foraging substrates as an enrichment device may prevent or reduce the incidence of cannibalism in laying hens.

For Additional Information Please Consult the Following References

Blokhuis, J.J.  1986.  Feather-pecking in poultry: its relation with ground pecking.  Applied Animal Behaviour Science, 16, 63-67.

Cloutier, S., Newberry, R.C., Honda, K., & Alldredge, J.R.  2002.  Cannibalistic behaviour spread by social learning.  Animal Behaviour, 63, 1153-1162

Huber-Eicher, B. & Wechsler, B.  1998.  The effect of quality and availability of foraging materials on feather pecking in laying hen chicks.  Animal Behaviour, 55, 861-873. 

Johnsen, P.F., Vestergarrd, K. & Norgaard-Nielsen, G.  1998.  Influence of early rearing conditions on the development of feather pecking and cannibalism in domestic fowl.  Applied Animal Behaviour Science, 60, 25-41.