How does hatchery stress affect the development of play behavior?

Play is a behavior mainly observed in young individuals that can differ greatly between species in both function and appearance. Presence of play indicates positive experiences in animals, making play a useful assessment tool for animal welfare. Commercial hatcheries expose chicks to several stressors that can affect both behavior and welfare. Unfortunately, our understanding of play behavior in chickens is still limited as only a few studies have been conducted.Therefore, the aim of this study was to describe the ontogeny of various play behaviors in modern laying hens and to investigate how stress affects play behavior in chicks. A total of 80 chicks were used whereas 40 were hatched at a hatchery and 40 were hatched under controlled conditions. The chicks were tested in groups of four in enriched test arenas twice a week during five weeks. Each test lasted 30 minutes and novel objects were placed inside the arena after 10 and 20 minutes. Behaviors were noted while analyzing videos from the experiment using one–zero sampling and later divided into the categories of solitary, social, and total play. A linear mixed model with repeated measures was used to investigate how treatment, age, and the interaction treatment*age affect play behavior. Chicks played more during certain ages and all forms of play showed a similar change with age over both treatments. The amount of play did not differ significantly between treatments but there was a numerical (non-significant) tendency for hatchery chicks to play more, which may indicate compensatory play