Hens with Benefits: Enrichments' Effects on Resilience in Laying Hens
The ability to me minimally impacted by stressors is a beneficial characteristic captured by the broad concept of “resilience”. In humans and laboratory rodents, environmental factors that improve affective state have been shown to also increase resilience. This has practical relevance to farm animal welfare because efforts to directly improve affective state may provide synergistic benefits by minimizing the negative impacts of aversive stressors. This thesis investigates if enrichments improve resilience in laying hens. Hens housed in Enriched environments, designed to promote more positive affective states, were compared to hens housed in Control environments which, in contrast, were designed to minimize both positive and negative affect. Resilience was inferred from a collection of measures chosen to represent two resilience components: appraisal and coping. I hypothesized that enrichment-based affective state manipulations would cause hens to appraise situations more positively and cope with aversive situations more effectively. Moreover, I hypothesized that individual hens would show stable, consistent response patterns across the different resilience measures, allowing them to be classified according to a unitary resilience construct. Enriched hens did exhibit relatively more positive appraisals of aversive stimuli (inferred from diminished defensive reflex responses); and showed improved coping after exposure to aversive stimuli (inferred from reduced autonomic stress responses and faster recovery). However, individuals did not show consistent response patterns across the different resilience measures. These findings are consistent with the hypothesis that improved affective state promotes resilience by facilitating more positive appraisals and making hens more effective at coping. But they do not support the idea that resilience, as a unitary construct, applies to laying hens. The results also suggest that improving laying hens’ environments can provide synergistic welfare benefits by directly improving affective state and by making hens less impacted by stressors. Thus, if these benefits can be realized in commercial settings with relatively low-cost enrichments, promoting resilience may provide a practical strategy for improving laying hen welfare.