The play chicks showed higher pessimism levels than the control chicks in the judgment bias test. Control chicks had a greater inclination to exhibit thigmotaxis in the novel arena test by moving along the edges of the arena and crossed more quadrants than play chicks. In contrast, play chicks interacted significantly more with the novel object and traversed more circles than control chicks to reach it.
There were no significant differences found between the play chicks and control chicks in weight measures, handling scores, social reinstatement, and tonic immobility tests. Similarly, no difference was noted in CORT levels before and after the restraint between the two groups. However, it is interesting to note that the control chicks had higher CORT values than the play chicks at all times, even though the values were not significant.
Providing environmental stimulation for animals can improve welfare, but our study found that play-enriched chickens took longer to reach stimuli in the judgment bias test, suggesting a more pessimistic behavior. This was unexpected as play sessions were thought to buffer against negative effects. It is unclear why this occurred and further studies are needed. Negative emotional states can lead to a more pessimistic judgment bias, and it’s possible that play-enriched chickens experienced increased frustration, leading to a negative emotional state.