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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. |
