Horses that have vices such as head-weaving and crib-biting may be troubled, but they are not cognitively impaired, the findings of Swiss research suggest.
Such behaviors are known as stereotypies – repetitive actions that have no discernible function. They include cribbing, head-weaving, stall walking and self-mutilation.
Behaviorists estimate they are seen in 10 to 20% of domestic horses, whereas horses in the wild do not exhibit stereotypies.
These repetitive behaviour patterns appear to arise during periods of chronic stress, with some genetic predisposition also found.
With domesticated horses, less-than-ideal keeping conditions and repeated experience of frustration are considered the cause, such as when the desire for exercise or food intake is only satisfied to a limited extent.
In cribbing, horses usually place their upper incisors on a stall fixture such as the feed trough, contract the muscles of their lower neck, and emit a characteristic noise or grunt.
One prominent hypothesis suggests animals affected by stereotypies are cognitively less flexible compared to healthy horses due to sensitization of a specific brain area, the basal ganglia.
The aim of this study was to test this hypothesis in cribbing horses and healthy controls using learning tasks which have been used to diagnose basal ganglia dysfunction.
The findings of the study, carried out by agriculture research agency Agroscope in collaboration with the University of Neuchâtel, have been reported in the journal Animal Cognition.
Agroscope researcher Sabrina Briefer Freymond designed a challenging four-part test with two reversal learning tasks to test the cognitive impairment hypothesis.
Six cribbing and seven control horses were used in the study at the Swiss National Study Farm, run by Agroscope.
The animals had to learn to distinguish two different-coloured symbols: a circle and a cross on a black or white background. The symbols were attached to two automatic feed flaps in random order.
Once they had recognised the correct symbol and pushed the right flap, they were rewarded with food.
After six successful performances in a row, the task was reversed. The feed flap with the symbol that previously produced no reward was unlocked, giving the horses access to the feed.
The rethink needed here to crack the challenge proved to be the most difficult learning step for the horses, requiring the most attempts.
Here too, however, the horses demonstrated their ability to succeed, managing to solve the second reversal task a good deal more quickly. In other words, they seem to be learning how to learn.
The results showed that all horses, both the cribbers and the control animals, were capable of solving the learning tasks.
In addition, no differences were detected in pulse or heart-rate variability.
“Cribbers learn this task as well as other horses,” Briefer Freymond said. “We were unable to detect any learning difficulties, which surprised us.
“The crucial difference between our study and earlier ones conducted by other researchers is that we allowed the horses to crib when they needed to.”
Briefer Freymond discovered in an earlier study at the Swiss National Stud Farm that cribbing horses are more sensitive to stress, and that for them, cribbing represents a stress-relieving strategy.
Moreover, the tasks were designed so as to maintain motivation and reduce stress, with the learning tests being limited to 20 tests twice daily.
What’s more, after three mistakes the animals were rewarded anyway, in order to maintain their enjoyment of problem-solving.
“Variety and the experience of success are important in work with horses,” she said.
The study team said their results challenge the widely held belief that crib-biting horses, and stereotypic animals more generally, are cognitively impaired.
“We conclude that cognitive under-performance may occur in stereotypic horses if they are prevented from crib-biting to cope with experienced stress.”
The study team comprised Briefer Freymond, Alice Ruet, Maurine Grivaz, Camille Fuentes, Klaus Zuberbühler, Iris Bachmann and Elodie Briefer.
Briefer Freymond, S., Ruet, A., Grivaz, M. et al. Anim Cogn (2019) 22: 17. https://doi.org/10.1007/s10071-018-1217-8