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Rearing experience and genetic strain affect fear response in laying hen pullets

2022 CPRF,Behaviour & Welfare
Fearfulness is detrimental to laying hens in non-cage housing systems and can reduce productivity, lead to injury, and increase mortality. We asked whether rearing complexity and genetic strain affect fearfulness in pullets. Four flocks of Lohmann Brown-lite (LB) and Lohmann Selected Leghorn-lite (LSL) were raised in either barren pullet cages (C) or one of three commercial rearing aviaries of low (A1), intermediate (A2), or high (A3) complexity during the brooding period. At 14 weeks of age, 688 pullets were exposed in pairs to a two-stage fear test. Pairs were placed into a circular novel arena (NA) marked as 12 zones with a novel food dish in its centre (Stage 1; 10 min) Then, a novel object (NO, coloured tube) was slowly lowered from the ceiling into the food dish (Stage 2; 5 min). Individual locomotion (zone changes) and alert behaviour (upright walking and standing, vocalizing, jumping, flying) in the NA were recorded in60 sec intervals. In the NO, the initial (e.g., active avoidance vs stationary) and secondary responses (e.g., approach; in 30sec intervals) were recorded per bird. Locomotion which suggests exploration, and alertness in the NA were analysed by fitting linear mixed models. Reaction to and approach of the NO were assessed by calculating odds ratios (OR) and hazard ratios (HR) respectively. NA test: Pullets raised in C explored less (p<0.001) and performed more alert behaviour (p<0.001) than A reared pullets. LB pullets showed more alert behaviour than LSL (p<0.001). NO test, initial response: LSL were 2.7 times more likely to actively avoid the NO than LB (p<0.001). A1 and A2 pullets were 6.4 and 3.3 times more likely than C and 3.6 and 1.9 times more likely than A3 pullets to actively avoid the NO (p<0.001). Secondary response: A1 pullets were 2.9 times, A2 3.4 times, and A3 4 times more likely to approach the NO than C pullets (p<0.02). Aviary pullets showed fewer fear responses than C in both the NA and the NO test by being less alert and showing a higher likelihood to explore the arena and approach the novel stimulus. Contrary to pullets raised in A1 and A2, both C and A3 pullets were stationary in response to the NO. C pullets stayed away, whereas A3 pullets recovered and approached, which suggests an adaptive behavioural response and less fearfulness. The two strains behaved differently in both test phases. In the NA LB pullets seemed more fearful, shown through more agitation. In the NO test, LB and LSL pullets displayed different initial fear responses with no difference in the secondary response. In conclusion, the complexity of rearing housing reduces fearfulness in laying hen pullets, while the effect of genetic strain seems dependent on the frightening stimulus.
Tags :
fear,genetic strain,rearing
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University of Guelph

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