Performance of laying hens in a cognitive bias task : effect of time since change of environment

Abstract: In the debate on laying hen welfare, and specifically housing conditions, the main focushas been on physiological and behavioural measures. What is lacking is knowledge of howthe hen experiences the situation – her state of mind.This study is an attempt to gain insight into the private mental states of former batteryhens. It uses a cognitive bias method based on spatial judgement, i.e. judgement of aambiguous stimulus placed spatially in between a reinforced and an unreinforced stimulus.This method has previously shown differences in judgement by animals in enriched versuspoor housing. The aim of the current study was to measure such biases expressed by henstwo months compared to four months after moving from battery cages to littered pens. Theanimals were also tested in a novel object task for a measure on general anxiety, and theirplumage condition was scored. Their social rank was established by testing penmates inpairwise competitions over a limited food resource.The hens showed longer latencies to reach the intermediate position four months afterleaving the cages, compared to two months after. Possible reasons for this could be that thepositive effects of the improved environment were largest when the hens had recently leftthe battery cages, with the effect of the improvement gradually being diminished or evenreversed. It is likely that novelty in itself is positive to hens, and a static environmentbecomes boring in time even though it is far more complex than a battery cage.No difference was found in the reactions to ambiguous cues by hens of different socialstatus. A strong correlation was found between feather score and social dominance.