Play is a self-motivated seemingly non-functional behavior mainly observed in young animals. Moreover, play behaviors can be divided into three categories; social play, object play and locomotor play. The type of activity the category contains varies, as play behaviors vary between species. Play behavior is seen as an indicator of positive emotions in animals, therefore play could be an indicator of welfare. However, the relationship between play and welfare requires further studies. In this study, information was compiled from various articles about play and its relation to welfare. Above all, the study focuses on welfare and play in chickens, as studies on chickens are most lacking. Play provides several benefits regarding motor training, social cohesion and cognitive training. Livestock such as calves, piglets and lambs have all been observed playing. No play has been confirmed in chickens which is mainly due to lack of research. However, play has been observed in other bird species, including birds within the order Galliformes. Amount and type of play varies depending on the environment, which suggests that animal welfare has a great significance for play. If no play occurs, one could conclude that welfare needs to be improved. Lack of play observed in chickens could be due to poor welfare or lack of research. After all, presence of play in other bird species increases the probability that chickens also play. Results indicate that play could be used as an indicator for welfare.

This diploma thesis is focused on animal play behaviour, it's features and factors that influence it. It also shows how play can be used as an animal welfare indicator and moreover that play may also improve welfare. Play is interesting from physiology and neurology point of view as well because it is able to trigger positive emotions. This thesis also describes the main hypotheses explaing evolutionary functions of play. The newest hypothesis claims that play may be a "training for the unexpected"(Špinka et al., 2001). Our experiments tested this hypothesis. We investigated if play of piglets before weaning could improve their coping with stress and reduce agonistic behaviour after weaning and later in life. Results show that play in an extra space before weaning does not influence pig's behaviour very much, but it seems to have some impact. Results also show other factors influencing agonistic behaviour of pigs - groupsize, gender and weight gain.