Horses do not exhibit motor bias when their balance is challenged

Abstract

In many equestrian pursuits such as dressage and show-jumping, it is important that the horse exhibits the same level of balance when ridden to the left as when ridden to the right in canter -that is, to show no motor bias. It is a long-held belief within such disciplines that to reduce bias that exists in horses and thus to enhance symmetry of performance to the left and right, the horse needs to be worked equally in both directions, although there is a lack of scientific evidence of this influencing bias. There also is little compelling evidence for either the existence or absence of motor bias in unridden (and therefore younger) or ridden (and therefore older) horses. In this study, we tested whether there was a difference in motor bias between unridden (n 5 15) and ridden (n 5 15) horses when their balance was challenged by cantering them in circles both to the left and to the right on the lunge. As indicators of a difference in balance between the left and right and thus as indicators of motor bias, we conducted three lunging tests -time spent in canter, whether the horse cantered on the correct lead and whether it became disunited. A grazing stance test, where the extended foreleg during grazing was recorded as the preferred forelimb, was also used to compare responses in a test where balance was not actively challenged, to the three lunging tests where balance was actively challenged. No bias was found in either the unridden or ridden groups when their balance was challenged, but ridden horses exhibited a motor bias in grazing stance -when their balance was not challenged. There was also a correlation between the responses in all three lunging tests, but none between the grazing stance test and any of the three lunging tests. We therefore conclude that neither ridden nor unridden horses are biased when their balance is challenged; thus it cannot be concluded that ambidextrous training affects an inherent bias, and that estimation of motor bias in horses is affected by the test conditions. Finally, if ridden horses are truly unbiased, strong human motor bias might be responsible for the common perception amongst riders that horses are biased.

From Science to Practice: A Review of Laterality Research on Ungulate Livestock

“…Together, these findings support the idea that social coordination is an important driving force for the evolution of population level laterality [3] and that population level motor laterality may be determined more by the nature of the tasks than their complexity [183]. Several motor laterality studies on horses have shown how humans may influence the expression of motor laterality in domestic species, for instance, through breeding and training [54,57,58,94]. For example, horses that were trained or ridden showed population level biases in locomotion and standing, while unridden and untrained horses had no population bias [54,58].…”

“…Several motor laterality studies on horses have shown how humans may influence the expression of motor laterality in domestic species, for instance, through breeding and training [54,57,58,94]. For example, horses that were trained or ridden showed population level biases in locomotion and standing, while unridden and untrained horses had no population bias [54,58]. However, other reports have suggested that training reduces laterality in locomotion [94], and since untrained horses are usually younger, age may also have played a role (see Section 4.4).…”

Is the left forelimb preference indicative of a stressful situation in horses?

“…In addition, thoroughbred-racing horses showed a population bias to place the left forelimb in front of the other forelimb during grazing (McGreevy and Rogers, 2005). These two measures of limb preference appear to be independent of each other since Wells and Blache (2008) found no association between forelimb preference while grazing and limb preference while cantering. On the other hand in feral horses, Austin and Rogers (2012) showed no population preferences to place one forelimb in front of the other during grazing, stressing the hypothesis that limb preference in domestic horses may be entrained by human handling.…”

“…In line with this work, McGreevy and Thomson (2005) population bias of forelimb preference while grazing than thoroughbreds, and Quarter Horses trained for cutting, which requires equal agility on the left and right sides, show no bias for the same measure. In addition, Wells and Blache (2008) reported a right population bias for forelimb preference while grazing in older horses (that had previously been ridden), whereas that was not the case for young horses (that had never been ridden).…”

Horses’ (Equus Caballus) Laterality, Stress Hormones, and Task Related Behavior in Innovative Problem-Solving

“…While the left hemisphere has been shown to be preferentially used for established learned responses, categorization of stimuli and approach behavior, the right hemisphere has been proposed as being dominant in information processing for emergency reactions, stress responses, novelty, and social interactions [29,30,31,32,33,34,35,36]. The motor laterality is assumed to be the result of brain hemispheric modulation through former experiences and training [27,37]. Sensory laterality may be independent of previous experiences and may change more flexible between left and right organ use with different tasks than reported for motor laterality [31,38].…”