Stress: The Different Types and Strategies to Reduce it in Your Horse

Horses, like us, are equipped to spend resources in fighting or fleeing external threats, and while this can result in high levels of stress, the short duration limits the cost to the animal’s resources. Indeed short-term stress can be beneficial, mobilizing the immune system and motivating an individual to conquer problems. For example, horses handle intense but temporary stress, like transport, surprisingly well. On the other hand, prolonged low-level stress exerts a much higher toll and leaves one vulnerable to illness, infections and other threats to mental and physical well-being. For many horses this chronic stress is embedded into their daily lives.

Here, I will explore what stresses horses out, what is probably manageable and what is not, look at the consequences of that unmanageable stress, and what we might do to alleviate it.

Transport Stress

Studies indicate that transport stress appears to peak in anticipation of transport and loading, and decreases once horses are on the road or in the air. Carolien Munsters of the Netherlands, studying nine horses during an eight-hour flight between The Netherlands and New York, found that physiological stress markers were higher during loading, taxiing and in-flight turbulence, but returned to resting levels during the flight. Interestingly, the least reactive horse exhibited the highest heart rate, suggesting that not every horse exhibits stress through obvious behavioural cues.

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Schmitt and colleagues studied transport stress in seasoned show horses travelling over two days and 1,370 km, from Saumur, France, to Germany for competition, and back. They found increased physiological stress indicators in anticipation of transport, and during all four shipping days. Levels decreased, however, throughout the day, and on each subsequent day, suggesting that horses do adapt to transport over time. Cortisol levels quickly returned to normal during an overnight rest. The authors emphasized the value of rest periods for long-distance transport.

Confinement Stress

Evolutionarily adapted for almost continual grazing over vast territories and periodically exploding with sudden bursts of speed to flee actual or perceived threats, horses are poorly equipped to spend upwards of 16 to 22 hours a day in isolated box stalls. Turn out into small individual enclosures does little to alleviate this innate desire to move. Indeed, stalls may be a great idea for humans, but they are a poor idea for horses.

Studies across the globe overwhelmingly come to the same conclusion that as the time outside of the stable increases, the rate of abnormal behaviours (such as cribbing, weaving, stall walking, etc.) decreases. These abnormal behaviours, or stereotypies, are generally thought to be indicative of compromised welfare and a reaction to prolonged, unavoidable stress.

Isolation Stress

Undoubtedly, confinement is difficult for horses, but it is the solitary aspect of that confinement that is particularly taxing. Compelling evidence comes from a study by Kelly Yarnell and her colleagues, who looked at horses’ physiological stress responses in four different housing situations (singly housed with no social contact, singly housed with partial contact, pair-housed with full contact, and group-housed with full contact). The “group-housed with full contact” horses not only experienced the least stress, they were also easier to manage than when singly housed. The study’s “repeated measures” design (i.e. the same horses participated in each of the four conditions) provides compelling evidence that increasing isolation was causing the same horses to become more stressed and less manageable (2015).

Similar findings come from a prospective study (i.e. following subjects over time) that examined the impact of first time stabling on 36 two-year-old, non-stereotypic Warmblood colts and fillies (Visser, Ellis, & Van Reenen, 2008). For 12 weeks, half the horses were housed in individual stalls while the other half pair-shared in larger stalls. Strikingly, by the study’s end, 67 per cent of the individually housed horses developed serious stereotypies such as cribbing and weaving, whereas none of the pair-housed horses did. Since none of the horses exhibited stereotypies at the study’s onset, this research provides another convincing causal link between social isolation and the development of stereotypies.

Food Deprivation

Not only were horses designed to move and live in social groups, but they were designed for almost continual grazing. Horses have high stomach acids for breaking down high-fibre food in a constantly full gut, but when there is nothing in the stomach to break down, the acids attack the stomach itself. Modern feeding practices that offer set meals, high in quality, but limited in quantity, leave the horse with long periods of an empty stomach and vulnerable to the development of ulcers. Hausberger and her colleagues noted that horses can experience gastrointestinal discomfort when deprived of food for as little as one or two hours.

Long bouts between eating also exerts psychological costs. When meals are consumed quickly, the isolated and frustrated horse is left with nothing to do and prone to the development of stereotypies. Stereotypies are thought to derive from a normal behaviour to satisfy a goal (e.g. grazing) that cannot be satisfied in the current environment. The resulting abnormal behaviour (e.g. cribbing) becomes an abbreviated version of what was once a purposeful and normal activity; as the stress is prolonged, the behaviour becomes repetitive, invariant, and chronic.

Stress and Depression

Besides the development of stereotypies, stress can also have consequences that are more subtle. In 2012, French researcher Carole Furieux observed the behaviour of 59 working school horses and noted that 24 per cent of these horses displayed a “withdrawn” posture (a stationary, atypical, flat-neck, unblinking, wide-open eyes with a fixed gaze, and fixed, backwards pointing ears). Compared to “not-withdrawn” horses from the same stable, withdrawn horses showed reduced responsiveness to human interaction, were indifferent to activity in the stable, but were more reactive to more challenging situations such as being faced with a novel object. Furieux described these horses as exhibiting a “behavioural despair” similar to human clinical depression. She then tested whether horses who looked clinically depressed were experiencing a key symptom of human depression, that of anhedonia – the loss of pleasure. Anhedonia has been explored in chronically stressed laboratory rats by measuring their reduced sugar intake. Lab rats, like humans, love sugar, but researchers can make them indifferent to sugar by exposing them to chronic stress and thus inducing a state of anhedonia. Assuming that horses, like rats and people, are also sugar junkies (research suggests that they are – generally preferring sugar solutions to plain water, sweet feed to unsweetened feed etc.), Furieux tested whether her “withdrawn” horses would voluntarily consume less sugar than non-withdrawn controls. Indeed they did just that, suggesting that perhaps they were doing so because life, even life with sugar, was just not that much fun anymore.

Learned Helplessness

When horses, like humans, face prolonged inescapable stress, they become vulnerable to the condition of “learned helplessness.” Martin Seligman, the researcher who first coined this term in 1967, trained research dogs to respond to the sound of a tone alerting them that the floor on which they were standing would soon become electrically charged. The dogs quickly learned to jump over a barrier to avoid the shock when they heard the tone. When Seligman then charged the floor on both sides of the barrier so that no amount of jumping would escape the aversive event, the dogs eventually ignored the warning bell, whimpered, and remained inert on the charged floor. When the escape route was reintroduced the dogs did not pursue it, although physiological measures attested to their acute distress. In other words, the dogs learned that they were helpless in the situation where there was a constant presence of aversive stimuli, accepted that they had no control, and thus gave up trying to avoid the situation.

Recently, researchers have suggested that horses may be particularly vulnerable to learned helplessness, although their suffering may not be readily apparent (Hall, 2008). Inexperienced riders who inadvertently give conflicting aids, or even experienced riders whose competitive drive may result in them missing subtle cues of discomfort, are equally likely to place a horse in the position where there is no correct answer. When behaviours have no impact on consequences horses may simply give up trying.

Seligman identified deficits in his dogs of passivity and depression that may well encapsulate the very behaviours that we value (consider the “bomb-proof school horse or show hunter, or western pleasure horse). Equine scientist Andrew MacLean notes that what trainers may mistake as submission, obedience and successful training, could more likely be a horse who has given up trying to escape from relentless conflicting pressure (2009).

Even with the best of intentions most of our horses living in modern day boarding and training facilities are experiencing stress. Whether that stress has surpassed their ability to successfully cope is a tricky question. Horses’ propensity to suffer silently makes it difficult to know how much is too much. And, chronically stressed horses may simply turn off responses when behaviours no longer have an impact on consequences. As owners, we are our horses’ only advocates and we are the ones who have to push to change industry norms and make a better life for our horses.

HOW DO I REDUCE MY HORSE’S STRESS?

Prepare for stressful events
The impact of intense short-term stressors, such transport, can be dramatically reduced by pre-training. Horses, like humans, learn by association: either associating two stimuli such as trailers and treats or trailers and a very bad event, or associating a behaviour and a resulting consequence, such as waiting patiently on the trailer results in getting off and going for a ride in the forest. Building positive associations with potential stressors, gradually over time, can turn these stress overload situations into welcome experiences.

Make food last longer
Although free pasture access remains the gold standard, there are viable alternatives that may be more easily accomplished in intensive systems. The industry standard of providing the finest quality hay may not be in the best interests of your horse, as it is consumed quickly and provided sparingly. Horses with higher energy requirements may need some of this fabulous hay, but it should be supplemented with higher fibre, lower calorie hay that will allow horses to munch throughout the day (Mazzola et al. 2016). Slow feeders, small holed hay nets, doubling and even tripling up small-holed hay nets, or providing a variety of hay choices in multiple locations all increase consumption time, leave the horse less vulnerable to ulcers, and more closely mimic grazing.

As with forage, making horses work harder to access their grain (e.g., adding stalky hay to the grain feed, placing smooth large stones in the bottom of the feeding tub, or using foraging devices that allow small amounts of food to fall out of a rolling ball) all increase feeding time and thus enrich the solitary stall environment.

Turn them out
With a good shelter, good footing and a good blanket, even high-end show horses can happily live out 24/7 in most weather conditions. Since lack of control is a key aspect of learned helplessness, giving horses some control over their environment, such as the choice to be in or out, leaves them less vulnerable to developing this condition (Hall, 2008).

Let them socialize
There is ample research to suggest that horses living in a natural stable herd form clear dominance hierarchies that are seldom contested and serve to minimize aggression rather than exacerbate it. (e.g. Ladewig, 2013). Upon the completion of a highly successful study where elite breeding stallions were turned out together during the non-breeding season, the Swiss National Stud continues to house this bachelor band every year. Lead researcher Sabrina Briefer-Freymond noted that stallions initially and briefly engaged in ritualistic behaviours (abbreviated, non-contact behaviours that substitute for actual aggression). There were no injuries, welfare was greatly enhanced and management costs significantly reduced.

Pre-exposure to potential herd mates (letting them meet over a fence), keeping the groupings consistent (new additions and even new subtractions upset the existing dominance relationships), keeping resources plentiful with multiple feeding stations, and initially removing hind shoes until hierarchies are established, all serve to lower risk in group or paired turn out.

Unfortunately, as one lonely voice at a boarding facility with multiple owners and potential litigious threats, you may not be able to shift “single-housing” thinking. You may still improve your horse’s isolated existence, however, by stable modifications that allow compatible neighbours to touch (e.g. removing electric wire between turn out paddocks, creating grilled windows between stalls, half walls, or half wood/half grill walls). Where stalls are separated with floor to ceiling wooden planks, gradually removing the upper planks so that eventually horses can put their heads into their neighbours stall is a cost effective way to increase interaction.

Antonia J.Z. Henderson, a psychology professor at Vancouver’s Langara College and equine psychologist, researches, teaches, consults and writes about human/animal relationships. She has owned, bred, imported and successfully competed her own horses in hunter/jumper and dressage, and has managed and taught at a number of hunter/jumper facilities.