Importance of the social environment for reproductive and general welfare of domestic horse (Equus caballus) stallions

The obligation to ensure the welfare of domestic horses is evident. Social bonds are an essential part of the daily life of feral horses. In human-controlled conditions, stallions usually live alone in a barren environment of individual boxes or paddocks with contact to conspecifics limited to visuals. Still, many stallions do not have regular access to paddocks and pastures. This provokes frustration and stress which has been shown to contribute to the development of stereotypies, self-mutilations, abnormal sexual behaviour and reproductive problems. This review highlights how domestic environments may negatively diverge from the natural conditions necessary for the healthy behavioural development of stallions. We address stallions' welfare and reproductive problems that may arise from their lack of social contact. These issues are discussed along the stages of a stallion's life under free ranging conditions. We postulate that today's breeding stallions must be enabled to enjoy the positive aspects of a bachelor stallion's life. This should include adequate consideration of the stallions' reproductive behaviour including contact with a sexually receptive mare. This will not only improve animal welfare but also ensure optimal semen quality and fertility. • Social bonds are an essential part of the daily life of feral stallions • In boxes, stallions may develop abnormal behaviour and reproductive problems • In the review, we address stallions' welfare and reproductive problems • We postulate the adoption of a bachelor stallion's life for breeding stallions