Selection for wheat digestibility affects emotionality and feeding behaviours in broiler chicks

In poultry farming, selection for high production, as for growth rate or feed efficiency, may be associated with risks for animal welfare. In this study, we tested whether divergent selection for a new trait linked to feed efficiency, i.e. digestibility, had correlated side effects on the behaviours of broiler chickens. Digestibility was assessed from apparent metabolisable energy values corrected to zero nitrogen balance (AMEn). We tested the behaviours of 80 broiler chickens from a divergent selection experiment for high (D+ line, 40 chicks) or low (D− line, 40 chicks) wheat digestibility. We used tonic immobility (TI), open-field and capture tests to evaluate the emotional reactivity of the birds. Social motivation was assessed with a runway test. Food consumption, food neophobia and exploration for food were also analysed. D+ birds had significantly longer duration of TI and latencies of the first step in the open-field and runway tests than D− birds. Our data thus suggest a higher emotional reactivity in D+ birds than in D− birds. On the other hand, D+ birds showed significantly lower latencies to approach novel food and were more willing to search for food in an open environment than D− birds. In the runway test, D− birds spent significantly more time away from the social stimulus than D+ birds. No significant difference was observed in the capture test results of the two lines. Feed consumption was significantly higher in D− birds than in D+ birds, but weight gain did not differ between the two lines during the first 3 weeks after hatching. Our results showed that selection indirectly affected different behavioural traits and different dimensions of fear behaviour. D+ birds expressed higher inhibition in novel environments (TI, open-field and runway tests) than D− birds. However, in the presence of food (novel food and exploration for food tests), the opposite behaviour was observed. Food rewards might have had a higher positive hedonic value in D+ birds than in D− birds and reduce D+ birds’ fear level. Behavioural differences as a result of divergent digestibility could potentially be due to ‘co-selection’ or genetic drift. Further investigations are needed to understand the underlying mechanisms and be able to select animals with genotypes associated with traits beneficial for both the environment and animal welfare.