Effects of genetic background and social environment on feather pecking and related behavioural characteristics in laying hens

Woldwide, but especially in Europe, poultry husbandry will undergo significant changes due to the prohibition of
both battery cage systems and beak-trimming. In laying hens, these changes will increase the risk of feather
pecking. Feather pecking is defined as the non-aggressive pecking towards the plumage of other birds. It may result
in feather damage and mortality due to cannibalism, which can be considered the ultimate phase of severe feather
pecking. Feather pecking may therefore have negative consequences for bird welfare and the economic situation in
poultry industry. To gain further insight in risk factors related to feather pecking, this thesis investigated the effects
of genetic background and social environment on feather pecking and related behavioural characteristics in laying
hens. In several experiments, behaviour, performance and physiology of cage-housed birds from pure-bred genetic
lines was studied in different social environments at different ages. Results indicated that birds from different purebred
lines show differences in feather damage due to severe feather pecking (an indicator for feather pecking) and
in their response towards a novel object. This indicates that it is possible to select against high levels of both feaher
pecking and fear related behaviour. The tendency to develop feather pecking was also related to the response
towards a novel object, although this relation differed between birds from different backgrounds and from different
ages. Other results showed that the response in the novel object test was also related to performance, which should
be taken into account if such a test would to be used in a breeding program. Feather pecking and fear related
behaviour were also affected by group mates (social environment): non-fearful birds became more fearful in
presence of fearful birds. This effect could only be established at 18, but not at 5-6 weeks of age. At adult age,
fearful birds showed more feather damage in presence of non-fearful birds, whereas the social environment during
rearing had no effect on the occurrence of feather pecking. This indicates that fearful behaviour predisposes adult
birds both to more easily develop and to be targeted by feather pecking. The changes in social environment were,
however, not accompanied by physiological changes in brain serotonine or dopamine activity. These neurotransmission
systems have been related to feather pecking. Results did indicate that the role of serotonin uptake
does require further attention. According to the results from this thesis, laying hens should be kept in behavioural
uniform groups to minimize the damage due to feather pecking. Additionally, reducing the expression of feather
pecking could be achieved by breeding against expression of fearful behaviour, but possible correlated changes in
performance should be accounted for. It remains to be investigated how the results with respect to social
environment can be translated towards more extensive systems, such as floor-housing.