Most people are either right or left-handed. It is thought that right-handedness is genetically controlled, but that environmental factors also influence whether someone will be right or left handed.
Most horses also appear to have a preference for working on the right or left rein. Until now it was not known whether this is due to the horse's innate preference or if it is a result of training and use.
Now research to be published shortly in Applied Animal Behaviour Science suggests that horses do indeed have innate right or left sidedness. The research, conducted by Dr Jack Murphy and his colleagues at the University of Limerick in Ireland, assessed forty unschooled Irish Sport Horses to see if they favoured the left or right side.
Twenty mares and twenty geldings, all about 4 years old, were used for the study. Only horses that had received minimal previous training or handling were chosen, to reduce the influence of training on the results.
The horses were challenged to see how they responded under certain conditions. Each horse was observed standing in a paddock. The leg that they moved first when they started walking or trotting was recorded. Most horses showed a preference for left or right. Twenty-one horses (52.5%) preferred to start with the right foreleg. Sixteen (40%) preferred the left foreleg. Three (7.5%) showed no preference.
The researchers observed which direction the horses chose to bypass an object in a passageway, either when walking free or when ridden. (A green plastic container, 2.4m across, was placed in the middle of a passageway - with just over a metre either side to pass through.) Most horses showed a preference for which side they passed the obstruction when walking free. They were fairly evenly divided - seventeen preferred to pass to the left and eighteen favoured passing on the right side. Only five horses (12.5%) had no preference as to which side they passed. Being ridden had little effect on the horses` response.
The horses were put in a stable with a deep bed and allowed to roll. Again, most horses had a preferred side towards which they rolled.
In all tests, the direction of the horse`s response was influenced by the horse's sex. Most female horses appeared to favor their right side. Geldings tended to prefer a left-sided response. Overall, about 10% of horses showed no preference.
According to Dr Murphy, recognising that a horse is left- or right-sided would allow the trainer to develop the weaker side, resulting in a more balanced horse. Knowing whether an individual racehorse is right or left sided may also help the trainer decide which course suits it best.
Traditionally horses are led from the left side. On stud farms brood mares and foals are often led out together, the foal from the left and the mare from the right. Dr Murphy suggests that it is worth considering leading young horses from both sides, perhaps on alternate days.
The findings also support the idea of sex-specific training regimes, using different training regimes for male and female horses.
For more details see: Idiosyncratic motor laterality in the horse. Murphy J, Sutherland A, Arkins S.Applied Animal Behaviour Science (2005) in press..