The development and causation of feather pecking in the domestic fowl.

Feather pecking in poultry consists of pecking directed at the feathers of other birds, sometimes pulling out and eating these feathers. It may result in severe damage of the integument of the birds, including wounds of the skin. Finally wounded birds may be pecked to death (cannibalism). About 30 years ago, when most poultry was kept in traditional floor systems, this behaviour was an important cause of mortality. Nowadays most birds are housed in small groups in battery cages in modern poultry houses and in The Netherlands they are usually beaktrimmed (partial amputation of the beak). This resulted somehow in a decreased mortality due to feather pecking. However, the effects of feather pecking may have become less fatal, the behaviour as such did not decrease and pecking still causes a lot of (feather) damage and feather pecking is still a problem in modern poultry farming. Firstly, the problem relates to animal welfare, which is clearly at stake for the pecked birds. Moreover, beaktrimming may counteract the occurrence of cannibalism and may prevent a lot of suffering, it is a painful operation which should be omitted if possible. Secondly, feather pecking is also economically detremental. Defeathering has a pronounced increasing effect on heat production, leading to an estimated increase of energetic needs between 5 and 20 % for laying hens in battery cages. The development and expected practical use of alternative systems for laying hens is also relevant with respect to feather pecking. As these systems often incorporate characteristics of traditional floor systems, this may enhance feather pecking. The present study was aimed at elucidating the basic motivation behind feather pecking and the process leading to it. In Chapter 2 pecking behaviour of birds on a litter floor was compared with that of birds on a slatted floor, from hatching until 17 weeks of age. The average frequency (per animal per hour) of pecking at conspecifics was 73.2 in groups on slatted floors and 27.8 in groups on litter. It increased over time in groups on slatted floors, whereas it tended to decrease in groups on litter floors. Moreover, in the latter pecking at conspecifics was much less damaging. Here about 20 % of the pecks was directed at particles on the plumage of other birds, which is relatively harmless, and about 25 % at feathers. In the groups without litter, these percentages were 1 and 55 respectively. Ground pecking frequency appeared to be about 6 times higher in groups on litter compared to groups on a slatted floor. At 17 weeks of age the experiment was continued by transferring half of the animals from each floor-type to the other type of flooring material. Most striking was that animals reared on litter and changed to slats, showed a strong increase of pecking at conspecifics (together with an increase in feather damage) and a strong decrease of ground pecking. Birds reared on slats and moved to litter showed a strong increase in ground pecking and the majority showed a decrease of pecking at conspecifics. In the latter birds, plumage recovered from the damage done to it in the first part of the experiment. It was concluded that the results supported the hypothesis that feather pecking evolves as redirected ground pecking. Experimental evidence to support this hypothesis is presented in Chapters 3 and 4. In Chapter 3 the motivation for groundpecking was experimentally varied in 6 week old female chicks, housed on litter. The same experimental procedure that stimulated ground pecking in chicks on a litter floor, appeared to stimulate feather pecking in chicks on a slatted floor. This supports the hypothesis that ground pecking and feather pecking share common causal factors. Chapter 4 takes another approach to test the same hypothesis. Here, again using 6 week old chicks, floor-type was suddenly changed from a half litter half slatted floor into a full slatted floor. The fact that groundpecking decreased and feather pecking increased again supported the above hypothesis. The redirection of ground pecking was described in both chapters in terms of incentive motivation theory. In this concept of motivation the role of incentive stimuli in inducing motivational states and in directing behaviour is emphasized. Specific characteristics of litter, a slatted floor or feathers which may affect their ranking as an incentive are discussed. Possibly visual, tactile or gustatory feedback signals play a role, as well as positive long-term effects of ingestion. Moreover, it was stated that the possibility to perform specific consummatory behaviour patterns, may also affect the validation of a substrate as an incentive. In relation to this it was also suggested that the possibility to perform groundscratching in combination with pecking, may add to the stimulus feedback. Obviously the animal's past experience with environmental stimuli is crucial in the validation of stimuli as incentive. In Chapter 5 the effects of early experience with litter were studied. Hens were reared on litter floors (20 groups) or on wire floors (20 groups) until 17 weeks of age. Then all groups were moved to pens with half litter half slatted floors. It appeared that feather pecking was less in litter reared hens compared to hens reared on wire. Also feather damage was less in the litter reared groups. It was concluded that experiences during rearing influence pecking preferences during the laying period. In the same experiment the effect of beaktrimming was studied. As the beak of the chicken has a variety of sensory receptors, beaktrimming is likely to result in sensory deficits. This may affect tactile discrimination and interfere with the validation of an object as an incentive for pecking. During the rearing period beaktrimmed birds showed a lower frequency of ground pecking as well as feather pecking, on litter as well as wire floors. During the laying period all groups showed the same level of ground pecking irrespective of beaktrimming or floor type. Beaktrimming only showed an effect on feather pecking in the wire reared groups. Here feather pecking reached a very high level, although it did not much harm to the plumage of the birds. It was concluded that beak trimming does not change pecking preference nor does it decrease pecking frequency. Beaktrimming is effective in reducing feather pecking damage. In Chapter 6, it is reported that a high housing density significantly decreases ground pecking and scratching in young domestic fowl. Although no serious feather pecking occurred, it is suggested that a high housing density stimulates the redirection of ground pecking which may result in the development of feather pecking. In the general discussion (Chapter 7) a regulatory model of ground pecking is presented, in which the role of incentives is incorporated. The motivation of pecking is discussed and it is concluded that pecking serves several functions such as energy supply, consummatory stimulation or information gathering. The model of ground pecking is modified to allow the incorporation of these different functions. On the basis of this model some suggestions for future research are made. In a last paragraph the risk of some husbandry factors in relation to the occurrence of feather pecking are discussed and some measures to prevent feather pecking are suggested.