Range use is related to free-range broiler chickens’ behavioral responses during food and social conditioned place preference tests

International audience

anglais. Free-range broiler chickens usually show an uneven spatial utilization of an outdoor range. Due to behavioral and cognitive between-individual differences, some animals may be driven to associate food and conspecifics more strongly to the barn, causing them to be less prone to explore the range. In this study, we aimed to understand how broiler chickens with different ranging levels (low- and high-ranging chickens) would behave under conditioned place preference (CPP) test situations. We used two cohorts conditioned to two natural rewarding stimuli: food and social companions. In a two-chambered apparatus, one cohort (n = 31, 16 high-ranging, and 15 low-ranging chickens) was conditioned to one chamber that always contained a cup with a food reward (mealworms), while the cup in the other chamber was always empty. The same design was also used with the second cohort (n = 31, 15 high-ranging and 16 low-ranging chickens), although instead of food, the reward was the physical presence of two conspecifics. During the testing trials, the animals had access to both empty chambers, and the time spent in each chamber was quantified. For the first day of the food CPP test, both the high- and low-ranging chickens spent significantly more time in the conditioned chamber, where they had previously found mealworms. During the following extinction days, the animals showed a gradual loss of their learned preference, increasing their immobility in the apparatus. High-ranging chickens were more immobile than low-ranging chickens, however, as their number of trials without moving was significantly higher. Unexpectedly, during the first day of the social CPP test, only high-ranging chickens showed a place preference. An overall place preference was observed only on the second day, with no chamber preference during the extinction days. Our results suggest that whether and how a stimulus-reward association occurs for free-range chickens may also be dependent on individual differences and the nature of the reward (food or social). Since associative learning occurs on a daily basis for farmed animals and the way individuals learn or value the reward varies, this research advanced our knowledge of animal behavior and individual cognitive differences that can be highly beneficial in improving animals' living conditions; this new understanding will allow for a more individualized approach to rearing broiler chickens in outdoor systems.