Group housing of horses is not very widespread, despite obvious advantages for their development and mental well-being. One often expressed rationale for this is that horse owners are worried about the risk of injuries due to kicks, bites or being chased into obstacles. To address this concern, we developed and validated a scoring system for external injuries in horses to be able to record the severity of a lesion in a standardized and simple way under field conditions. The scoring system has five categories from insignificant loss of hair to severe, life threatening injuries. It was used to categorize 1124 injuries in 478 horses. Most of these horses were allocated to groups to study the effect of group composition (i.e. same age or mixed, same gender or mixed, socially stable or unstable groups) on behaviour and injuries. The material included mainly riding and leisure purpose horses of different breeds, age and gender. Most injuries occurred the day after mixing. Injuries of the more severe categories 4 and 5, which normally would necessitate veterinary care and/or loss of function for some time, were not observed at all. The minor injuries categorized as 1-2 counted for 99% of the total injuries. A few category 1 injuries were found on most horses, some horses had none injuries at all, and a few had many. Category 3 injuries (a minor laceration and/or contusion with obvious swelling) were only recorded in a baseline subset of 100 riding horses, there comprising 4% of the injuries. Whereas most of the injuries were found on the body, the category 3 injuries were mainly found on the limbs and head. The reason for this is probably that the skin there is tight and thus is more easily lacerated. Icelandic horses tended to have fewer and less severe injuries compared to other breeds. There was also a breed effect on location of the injuries. We conclude that the risk for serious injuries when horses are kept in groups is generally low and fear of injuries should not be a reason to prevent horses from social interaction with other horses. However, we emphasize that most of our recordings were performed during the summer period, and many horses were unshod. The situation might have been different in winter, and special caution should be taken if mixing horses shod with ice studs.
Proceedings of Equi-meeting Infrastructures: Horas National Du Lion D'angers, 2014, p. 20-25