Effect of Environmental Complexity and Stocking Density on Fear and Anxiety in Broiler Chickens

Simple Summary Broiler chickens are conventionally housed in monotonous environments at high stocking densities, which can negatively affect their welfare. This study evaluated the impact of environmental complexity and stocking density on anxiety and fear in broilers. Through behavioral testing, we found that broilers housed at higher densities responded less fearfully than those housed at the lower density, which is contradicting to expectations and previous research. Broilers housed in complex environments exhibited responses consistent with reduced anxiety compared to broilers housed in monotonous environments, suggesting improved welfare for broilers housed in the complex environment. Barren housing and high stocking densities may contribute to negative affective states in broiler chickens, reducing their welfare. We investigated the effects of environmental complexity and stocking density on broilers' attention bias (measure of anxiety) and tonic immobility (measure of fear). In Experiment 1, individual birds were tested for attention bias (n = 60) and in Experiment 2, groups of three birds were tested (n = 144). Tonic immobility testing was performed on days 12 and 26 (n = 36) in Experiment 1, and on day 19 (n = 72) in Experiment 2. In Experiment 1, no differences were observed in the attention bias test. In Experiment 2, birds from high-complexity pens began feeding faster and more birds resumed feeding than from low-complexity pens following playback of an alarm call, suggesting that birds housed in the complex environment were less anxious. Furthermore, birds housed in high-density or high-complexity pens had shorter tonic immobility durations on day 12 compared to day 26 in Experiment 1. In Experiment 2, birds from high-density pens had shorter tonic immobility durations than birds housed in low-density pens, which is contrary to expectations. Our results suggest that birds at 3 weeks of age were less fearful under high stocking density conditions than low density conditions. In addition, results indicated that the complex environment improved welfare of broilers through reduced anxiety.