Can horses suffer from depression too?
14 Mar 2015
In humans, clinical depression is diagnosed by the occurrence of a variety of symptoms. One of these symptoms can be anhedonia- the loss of pleasure.
Anhedonia has been successfully modelled in rats using sugar intake as an indicator of ability to feel pleasure, therefore some French and Canadian researchers thought they would see if they could model anhedonia in equines.
The study was conducted on twenty horses kept at a riding school in Western France. The horses were stabled and spent 4-12 hours a week being used for lessons and two days of the week turned out in a paddock and rested. Sugar blocks were fixed to the horses’ stalls and the amount of sugar each horse consumed over a thirty hour period was measured. The horses were fed an adequate diet, such that consumption of the sugar blocks would not be related to hunger.
As well as consumption of sugar, time spent displaying sterotypic behaviours, another sign of stress or boredom, was also recorded. Stereotypic behaviours included: crib biting, lip play, tongue play, lip or teeth rubbing, weaving, head shaking and nodding. The researchers noted, from a previous study, that some stabled riding horses display withdrawn states of activity and low responsiveness that seem to indicate little interest in their surroundings and could be a further symptom of depression. Therefore time spent in a withdrawn state was also observed and recorded. The withdrawn state was defined as “a stationary, atypical flat-necked posture; wide open unblinking eyes with an apparently fixed gaze and backward pointing ears.”
As hypothesised, the horses that spend the most time in the withdrawn state also had the lowest sugar consumption. Time spent being withdrawn correlated with time spent enacting stereotypic behaviours, a possible sign of chronic stress. Nine of the horses never displayed the withdrawn state at all.
Causes of depression could include: limited opportunity for social interaction with other horses, chronic stress, chronic pain or traumatic life events.
The researchers note that, “All these findings still do not demonstrate with certainty that horses… can become clinically depressed: the quality and quantity of the current evidence are not yet sufficient to conclude this. However these data are sufficiently consistent with this hypothesis to make additional research very worthwhile…”
Fureix, C., Beaulieu, C., Argaud, S., Rochais, C., Quinton, M., Henry, S., … & Mason, G. (2015). Investigating anhedonia in a non-conventional species: Do some riding horses Equus caballus display symptoms of depression?. Applied Animal Behaviour Science, 162, 26-36.