Is the left forelimb preference indicative of a stressful situation in horses?
Introduction
Limb preference has been reported in vertebrates (Vallortigara et al., 1999, Bisazza et al., 1998) including several mammals during different tasks (Rogers et al., 2013, Rogers and Andrew, 2002). Since each limb is controlled by the opposite brain hemisphere, limb preferences bias in vertebrates may indicate preferences to use the hemisphere opposite the preferred limb (Rogers, 2009, Vallortigara et al., 2011, Macneilage et al., 2009). In primates, the selective activation of one hemisphere is required to perform particular tasks, as for example the use of the right hemisphere/left-hand during difficult spatial tasks (Rogers et al., 2013). On the other side, limb preferences shown during simple tasks (i.e. tasks which can be performed easily and readily by either the right or the left hemisphere/limb) may reflect an individual's preference to activate a particular hemisphere, and hence to express a particular set of behaviour (Rogers et al., 2013). In non-human primates, for example, marmosets (Callithrix jacchus), which use preferentially their left hand to pickup pieces of food from the floor, are more fearful of novel environments (Cameron and Rogers, 1999) and fear-inducing stimuli (Gordon and Rogers, 2010).
In mammals, weaker paw preferences in tasks that required dogs to stabilise a container while licking food from it was associated to a strong stress response to certain sounds like thunderstorms (Branson and Rogers, 2006); dogs with no significant paw preferences to wipe a piece of tape from the nose also displayed higher levels of one of the stress hormones, adrenaline, some days after immunostimulation (Siniscalchi et al., 2010a).
Hemispheric specialisations in horses have been shown at both motor and sensory levels (McGreevy and Rogers, 2005, Austin and Rogers, 2012). Limb preferences have been reported in different breeds: in particular, a right bias for the leading limb used in initiation of galloping was observed in a large number of racehorses of various breeds at the population level (90%) (Williams and Norris, 2007). 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. Also similar to feral horses, the Przewalski horses (the closest undomesticated relative of Equus caballus) showed no significant forelimb preference (Austin and Rogers, 2014). In line with this work, McGreevy and Thomson (2005) found that standard bred trotting horses, which are handled on both sides, show a weaker leftwards 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).
Since motor laterality can be task-dependent and limb preference is associated with reactivity in different species (summarised by Rogers, 2009), here we investigated possible lateralisation in the first limb use in 14 Quarter Horse during different motor tasks (walking, stepping-off, stepping-on, truck loading and unloading) and its association with behavioural response (i.e. reactivity).
Section snippets
Animals, management and experimental design
Fourteen Quarter Horse, homogeneous for live weight (500 ± 25 kg), body condition score (3 ± 0.25 arbitrary units; Martin-Rosset, 1990) and age (6 ± 1 years), were recruited in this study. All horses were in good health status and each had been handled and trained for reining competitions. The research was carried out in a horses-stall in Corato (Italy), horses were housed in a “open air” stable which contained 20 single stalls (10.5 m2) in two rows, with a central aisle (3 m wide). All horses were kept
Forelimb preference
The %Res revealed that no subjects habituated to the test paradigm during the first seven presentations but a pronounced decrease in the %Res was observed in the last three presentations (see Fig. 1). All the data were subsequently analysed using only the first seven presentations.
As to the Laterality Index of forelimb usage a significant main effect of task type was observed (GLM = F(4,44) = 3.021, P = 0.028). Post hoc analysis (Fisher's protected LSD) revealed that this effect was due to the LI of
Discussion
Results revealed that forelimb preference in Quarter Horses is task dependent, with the preferential use of the left forelimb during stepping-off and truck-loading tasks. Truck-loading is considered to be one of the most stressful components of transport (Waran, 1993); fear of entering into a closed space as well as the height of the step up onto the ramp and the instability and incline of the ramp, all combine to a fear of loading (Houpt and Leib, 1993). Given that in vertebrates, individual
Conflicts of interest
The author declares no conflict of interest.
Acknowledgments
The authors are grateful to the trainer, Michele Lampo, and the horse stall owner, Antonella Urbano, for their valuable help during this study.
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