A Swiss study challenges the assumption that crib-biting horses are less flexible thinkers than their counterparts who don’t display such abnormal repetitive behavior.
Crib-biting is a well-studied stereotypy in domestic horses. It appears to help individuals to cope with stressful situations.
One prominent hypothesis suggests that animals affected by stereotypies are cognitively less flexible compared to healthy controls due to sensitization of the basal ganglia, an area of the brain.
However, a study carried out by Agroscope’s Swiss National Stud Farm in collaboration with the University of Neuchâtel found otherwise.
Researchers found that cribbing horses perform just as well in complicated learning situations as healthy controls. All horses in the study were able to recognise symbols as well as solve inverse conclusion exercises, which are difficult for horses.
The critical factor was that the cribbers were allowed to crib while performing the tasks, thereby relieving their stress.
Cribbing in horses has no obvious function. Cribbers 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. Horses in the wild do not exhibit stereotypies such as cribbing.
These abnormal behaviour patterns are found to arise during periods of chronic stress, and owing to a genetic predisposition.
With domesticated horses, sub-optimal living conditions and repeated experience of frustration are often the cause, such as when the desire for exercise or food intake is only satisfied to a limited extent.
For the study, Agroscope researcher Sabrina Briefer Freymond designed a challenging four-part test with two reversal learning tasks to determine whether certain regions of the brain are impaired in cribbers, with a consequent limiting of various learning outcomes.
In the study, conducted with six cribbing and seven control horses, 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 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 seemed to be learning how to learn.
The results showed that all horses – cribbers or not – were capable of solving the learning tasks. The study team did not find any performance differences across groups: both stereotypic and control animals required a similar number of trials.
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 had found in an earlier study conducted by the Swiss National Stud Farm that cribbing horses were more sensitive to stress and that, for them, cribbing represented a stress-relieving strategy.
In the latest study, the tasks were designed to maintain motivation and reduce stress, with the learning tests being limited to twice x 20 tests 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,” Briefer Freymond said.
Reporting on their findings in the journal Animal Cognition, the research team said: “Our results challenge the widely held belief that crib-biting horses, and stereotypic animals more generally, are cognitively impaired.”
However, cognitive underperformance may occur in stereotypic horses if they are prevented from crib-biting to cope with experienced stress.
Stereotypic horses (Equus caballus) are not cognitively impaired.
Briefer Freymond S, Ruet A, Grivaz M, Fuentes C, Zuberbühler K, Bachmann I, Briefer EF.
Anim Cogn. 2019 Jan;22(1):17-33. doi: 10.1007/s10071-018-1217-8. Epub 2018 Oct 17.