Are you right-handed or left-handed? When you take a step, do you start with your right or your left foot? And does your “motor laterality” reflect the way you think and feel? It appears to in horses.
In a study published in the journal Animals1, Isabell Marr, MSc; Kate Farmer, MA; and Konstanze Krüger, PhD, found a link between “motor laterality” and “cognitive bias”; right-sided horses tended to be optimistic and left-sided horses were more pessimistic. Asymmetry in a horse’s limb use predicted positive and negative thinking, a finding that has practical applications to animal welfare science.
What is motor laterality bias?
A left-handed person could be said to have a left-forelimb motor bias. Horses also show forelimb biases that your farrier might discover from the hoof wear patterns. When your horse lowers its head to graze, the same forelimb is often positioned in front. In this resting state, Thoroughbreds appear to have a left-forelimb bias whereas Quarter Horses are more ambilateral.2
Motor laterality bias is of interest to researchers because it has been linked to emotional state and temperament. For example, in a stressful situation like trailer loading, horses were more likely to take the first step using their left forelimb and also show stress behaviors. A left-forelimb bias was not seen when the horses were simply walking, suggesting a link between motor laterality and negative emotions.3
In their study Marr, Farmer, and Krüger included three different measures of motor laterality: the leading forelimb while grazing, the initial forelimb used when walking, and the forelimb held forward when exploring a box. All have been used in previous research, but the results haven’t been consistent with one another, and the best measure of motor laterality in horses isn’t clear.
What is cognitive bias?
Is the glass half-full or half-empty? Your answer might be viewed as optimistic (half-full) or pessimistic (half-empty), reflecting your positive or negative cognitive bias. Cognitive biases help an individual make a decision when not enough information is available, but these judgments are subjective, influenced by the situation, past experience, and personality.
To study cognitive bias in horses Marr and her colleagues used a procedure called location discrimination training. The horse was free to check out a box positioned in front of it either on the right or left side, and the researchers measured how quickly the horse approached the box from a fixed starting point. Which side the box was on alternated randomly between right and left. The horses were motivated to approach the box, because sometimes it was baited with food. For half of the horses, if the box was on the right side it always had food, but if the box was on the left side it was always empty. The side with food was reversed for the remaining horses.
After completing ten training trials every day for six days, all 16 horses had figured it out. They were much faster to approach the box with food and many stopped approaching the empty box altogether. The horses had learned to discriminate based on the box’s location, which is a fairly easy task for many animals.
The test for cognitive bias came next. What would the horse do if the box was placed in a new location directly in the middle, without any previous experience to guide its actions? Would the horse behave “optimistically” and approach the box quickly? Or would it behave “pessimistically” and approach the box slowly or not at all? From this study and others, we know that when the box is placed in this ambiguous middle location individuals behave differently; “optimists” will approach quickly as if they expect to find food and “pessimists” will approach slowly as if they expect the box to be empty.
How is motor laterality related to cognitive bias?
One of the research team’s key discoveries was that a horse’s forelimb preference predicted its cognitive bias. Horses who walked off taking their first step with the right forelimb were optimistic, approaching the box in the ambiguous middle location quickly. Horses with a left forelimb preference were pessimistic, approaching the middle box more slowly or not at all.
In this study, horses were in a familiar location walking toward a box that frequently contained food, and most (12 of 16, or 75%) showed a right-forelimb preference. Did the low-stress activity influence the disproportionate number of horses with a right-sided bias? Other studies have reported a more even ratio of left and right forelimb laterality in horses, and one found a left-forelimb bias when horses were in a stressful situation.3
Is motor laterality a useful welfare indicator?
At this point you might be tempted to rush to the barn curious to find out if your horse has a right or left forelimb preference and if she is an optimist or pessimist. Knowing how our horses think and feel is important, but this research was motivated by a more-worthwhile purpose.
One goal of welfare science is to accurately assess an animal’s emotional state. Equine welfare is typically gauged by the absence of negative indicators (rather than by the presence of positive indicators), as Marr and her colleagues point out. Pessimistic cognitive bias has been linked to poor welfare and negative emotional state, including anxiety, fear, and depression. Optimistic cognitive bias is a promising measure of positive animal welfare, especially since an individual’s degree of bias can change with the situation and recent experience. For example, a horse in an unfamiliar environment might show a pessimistic bias, which could be a situational effect rather than a fixed character trait.
The results of Marr, Farmer, and Krüger’s study are particularly intriguing because, not only do they build on existing research in horses, they also mirror similar findings in other species. For example, left-pawed dogs are more pessimistic than right-pawed or ambilateral dogs.4 Measuring cognitive bias takes a lot of time, but motor laterality could offer a simple, practical indicator of positive welfare if further research confirms that an animal’s right-limb-use bias is reliably linked to its positive emotional and cognitive state.
1Marr, I., Farmer, K. & Krüger, K. Evidence for Right-Sided Horses Being More Optimistic than Left-Sided Horses. Animals 8 (2018) 219; doi:10.3390/ani8120219.
2McGreevy, P.D. &Thomson, P.C. Differences in motor laterality between breeds of performance horse. Applied Animal Behaviour Science 99 (2006) 183–190.
3Siniscalchi, M., Padalino, B., Lusito, R. & Quaranta, A. Is the left forelimb preference indicative of a stressful situation in horses? Behavioural Processes 107 (2014) 61-67. https://doi.org/10.1016/j.beproc.2014.07.018
4Wells, D.L., Hepper, P.G., Milligan, A.D.S, & Barnard, S. Cognitive bias and paw preference in the domestic dog (Canis familiaris). Journal of Comparative Psychology 131 (2017), 317–325.