Stereotypies: What Causes Them, What They do, and More

Stereotypies, such as cribbing and weaving, are repetitive behaviours that follow a ritualized, invariant sequence and appear to serve no obvious purpose. Bizarre as many stereotypies appear to be, they are all components of a normal behaviour that has been isolated from its external goal or function, and which the animal is highly motivated to perform. Weaving for example, may originate as a thwarted, and now abbreviated, walking sequence where a stall-bound horse is prevented from reaching his intended goal (companions, feed or movement). A weaving horse remains stationary, but shifts weight between the forelegs or, in some cases, among all four legs, which eventually develops into a highly stylized, repetitive sequence.

In common horse parlance, stereotypies are often referred to as “stable vices,” although, as I will argue, the defects are more relevant to the management practices that precipitated them than to any malevolence on the part of the horse. Indeed, since stereotypies have never been observed in free-ranging feral horses, nor in other equids, such as zebras and donkeys, yet are seen at rates of three per cent to 34 per cent in domesticated horses, stereotypies have more aptly been named “the disease of domestication” (Marsden, 2002).

What Causes Stereotypies?

Simply put, we do.

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What Causes

Horses were designed to live in herds, form social bonds, often for life, and traverse large distances grazing almost continuously on mid- to poor-quality forage. In contrast, many of today’s horses are housed individually, possibly able to see other horses, but rarely to touch them, with limited or no turnout, and fed rapidly-consumed, high-quality, concentrates in measured feedings. In spite of 6,000 years of domestication, a horse’s biological need to move, to forage and to form strong social bonds with other horses has not fundamentally changed. The development of stereotypies is but one manifestation of this mismatch between what the horse was evolutionarily designed to do and the environmental challenges he faces within our current equine husbandry practices.

What Do Stereotypies Do?

Although stereotypies are defined as lacking an obvious purpose, much research suggests that stereotypies may offer the horse a degree of perceived control and a protective buffer against psychological distress in an adverse environment. This helps explain the very repetitive nature of stereotypies, as this repetition produces a predictable and beneficial neural feedback loop. It also explains why the behaviour continues even after the suboptimal conditions that precipitated them have been alleviated – the goal of the stereotypy is the performance of the activity itself.

Although the precise relationship between stereotypies and beta-endorphins is still unclear, research with horses and other species (including children with Autism) suggests that many stereotypies cause an increase in endorphins that provide a calming, stress-reducing effect. Dodman and colleagues found that when cribbing horses were treated with Naxalone, (which blocks the endorphin high), cribbing was reduced by 84 per cent. Cribbing bouts are also associated with lower heart rate and reduce cortisol concentrations, lending further support for the adaptive function of this stereotypy. Some equine researchers have proposed that horses with stereotypies may be better off than their stable mates who live in a similarly stressful environment, but lack the coping mechanism to ameliorate it.

Are Stereotypies Harmful?

An advertisement for one cribbing collar, which delivers an electric shock upon contraction of the horse’s neck muscles, states that cribbing is “a potentially fatal condition…a debilitating habitual behaviour leading to digestive problems, stomach ulceration and severe loss of condition.” Similar claims appear in many advertisements for potential cribbing “cures.”

Certainly stereotypic behaviour is not desirable. Cribbing can cause excessive tooth wear and may be related to weight loss in cases where the horse spends more time cribbing than eating. And, it is true that researchers have found an association between cribbing and ulcers. This relationship, however, is likely working in the opposite direction to that stated in these advertisements.

Current intensive management systems leave horses vulnerable to equine gastric ulcer syndrome (EGUS), the result of an imbalance between the protective and acid-producing functions of the stomach. Horses, with a gut designed for almost continual grazing, produce gastric juices constantly. When there is no buffering food or saliva in the stomach, the protective stomach tissue is eroded. Cribbing increases salivary flow and may provide some defense against the acidity of gastric juices (Nichol, 1999). Thus, cribbing may be an effect of ulcers and the resulting vulnerability to colic, rather than a cause. Direct evidence of stereotypies causing major health detriments is sketchy at best, and often the “cure” is considerably more harmful than the behaviour.

What Do We Do About Them?

Equine researchers unanimously agree that preventing stereotypies from developing will always be more effective than trying to eliminate them once they have become established. Over time, stereotypies are said to move into “central control,” which means they become emancipated from the original conditions that caused them. The stereotypy, now independent from its original trigger, is performed more readily, in more diverse situations, and becomes extremely resistant to modification. Still, there are environmental changes we can make that will improve psychological well-being for all the horses in our care, stereotypic or not.

Feed less lovely hay, and lots of it
High-quality hay may be necessary depending upon the horse’s energy requirements, but should be supplemented with a higher fibre, less rich hay to allow horses to eat for longer periods, and satisfy their evolutionary need for around-the-clock grazing. Slow feeder mangers and small-holed hay nets also allow for longer foraging without contributing to obesity.

Reduce or eliminate concentrates
Palatable grains seem to be involved in the complex relationship between stereotypies and endogenous opiates, both of which promote dopamine production and seem to exacerbate cribbing behaviour. Where concentrates are necessary to meet sport horses’ energy requirements, pre-feeding hay before grain (or, better still, feeding free-choice hay) appears to reduce cribbing duration and intensity by easing stomach acids, reducing gastric pain and making the horse’s need to crib less urgent (Nichols, 2013).

With weanlings, less is more
Weaning places youngsters at high risk for developing stereotypies. Good management for youngsters means “less management” – less weaning interference, less confinement and less grain. In a study of breeding farms in North America, Europe and Australia “natural weaning,” where mares weaned the foals themselves, was associated with a decreased incidence of stereotypies in the foals (Parker et al., 2008). Confinement, even part-time, makes weanlings much more likely to develop stereotypies than those living in paddocks or pasture (Heleski, 2002; Waters, 2002; Parker 2008). Feeding concentrates to weanlings is also problematic. Foals fed concentrates after weaning have been reported to be four times more likely to become cribbers than those who are not (Waters, 2002).

Apartment, condo, or single-family dwelling?
Studies across the globe overwhelmingly come to the same robust finding that as the time outside of the stable increases, rates of stereotypic behaviour decrease. And although confinement is stressful for horses, it is the solitary nature of that confinement that takes the real toll on these highly social animals. The fact that stereotypies are almost never seen in PMU mares (mares used for urine collection to make estrogen supplements), who live in highly restricted tie-stalls, but can touch and interact with neighbours, speaks to fact that tactile companionship may be even more important than freedom (Houpt, 2001).

In a convincing longitudinal study, Visser and colleagues (2008) examined the impact of first time stabling in 36 two-year-old, non-stereotypic, Warmblood colts and fillies. For 12 weeks half the horses were housed in individual stalls while the other half pair-shared a larger stall. Strikingly, by the study’s end, 67 per cent of the individually stalled horses developed serious stereotypies such as cribbing and weaving, whereas none of the pair-housed horses did so. This prospective study draws a causal link between social isolation and development of stereotypies, since none of the horses exhibited stereotypies at the study’s onset.

In short, housing horses in individual stalls is a great idea for humans, and a poor idea for horses. As equine researcher H.P. Davidson commented, “Stabling our horses usually benefits only one half of the horse-human relationship – the human.”

Let them touch
Stabled horses’ welfare can be greatly improved with designs that allow them to touch one another (e.g. grilled windows between stalls, half walls, or half wood/half grill walls). Cooper and colleagues eliminated weaving in a group of chronic weavers when the horses were housed in stalls that were open on all sides, allowing them to interact with compatible neighbours.

Let them have friends
Group or paired turnout, even for stallions, reduces stereotypies, improves welfare, reduces housing costs and may not be as “out there” as one would suppose (Vandierendonck, 2013; Ladwig, 2013). Horses have evolved to avoid aggression and embrace affiliation. To live successfully in a herd, horses developed an interactive repertoire that would avoid expending energy fighting for resources. Dominance hierarchies are formed quickly, usually understatedly, and once established, conflict is rare (Davidson, 2002).

At the Swiss National Stud, Sabrina Briefer Freymond (2012) successfully pastured five to eight elite (and expensive) breeding stallions together during their non-breeding season. Stallions first met in adjacent stalls, were pastured away from mares, with multiple feeding stations, hind shoes were removed before the initial encounter and herds remained stable throughout the season. Although there was some initial posturing, there were no injuries, welfare was greatly enhanced, and housing costs dramatically reduced. The study was so successful that the Swiss National Stud continues to pasture this “bachelor band” every year.

Where owners are still not convinced about their horse buddying up, research suggests that singly-housed horses may benefit from the companion they meet in a mirror. In a group of confirmed weavers and head shakers, McAffee and colleagues found that the installation of a 1mx1.5m acrylic mirror eliminated these stereotypies entirely. Furthermore, the effect lasted over the study’s five-week duration, even when the horses transitioned to a winter schedule of very limited turnout. Whether horses interpret the mirror image as a new friend or simply benefit from the perception of increased space is not clear. The low cost and easy installation, however, make mirrors an environmental enrichment worth pursuing.

Horses are hard-wired to form social bonds. When other horses are not available, they will make do with just about anyone else – donkeys, goats, dogs, cats and humans. Researchers have found that vigourous wither grooming that mimics the wither-to-wither “allogrooming” that horses do with each other, reduces heart rate, lowers cortisol levels and produces a calming effect for horses. A good long curry has many more benefits than the resulting shiny coat it produces, and provides yet another low cost, easily implemented modification we can make to improve equine welfare.

Don’t isolate: horses don’t commit copy-cat crimes
Cribbing, in particular, has been implicated as being “contagious.” Research indicates, however, that horses do not generally learn stereotypies from one another. In the rare cases that a horse exposed to a cribber begins to crib himself, he still needs a reason to do so. If the predisposing conditions are absent, it is unlikely that a naïve horse will begin cribbing simply from watching a neighbour. The unfortunate consequence of this belief, however, is that cribbers are often isolated, exacerbating their condition and further compromising welfare.

Be a nice boss
Although it is unlikely we will change our riding discipline in order to improve our horse’s welfare, the kind of rider we are, particularly in disciplines where the horse-to-human interaction is intense, may have an impact on the development of stereotypies.

In a study of 76 French Warmblood geldings, housed in in identical conditions (individual stalls, no turnout, and ridden for one hour a day), Hausberger and colleagues found that type of work was a significant factor in the development of stereotypies (2009). In this intensely managed facility, an astounding 65 of the 76 horses showed some evidence of stereotypic behaviour. Strikingly, although all horses experienced the same contained environment for 23 hours a day, the work they did for one hour a day mattered. The authors suggest that the degree of potential interpersonal conflict with their “bosses” (riders) in each of these disciplines may explain this pattern. Dressage horses, who experience the most controlled and intense interaction (and thus the greatest potential for interpersonal conflict) with their “boss,” presented the highest incidence and most serious of stereotypies. Vaulting horses, who experienced the least human intervention, exhibited the fewest and mildest stereotypies.

Provide a safe ‘injection site’
A common method of dealing with stereotypies, particularly cribbing, is to physically prevent the behaviour from occurring. Removing surfaces on which horses can crib, application of repellents or electric wire, punishing the horse with yelling, hitting or water jets, applying muzzles or cribbing straps, isolation and even surgically cutting a portion of the spinal nerve have all been proposed and practiced as viable solutions. Nearly all equine researchers concur that none of these devices address the underlying cause of the behaviour and thus further compromise equine welfare.

The effectiveness of cribbing collars is also dubious. Although they may reduce or eliminate cribbing while they are on, they actually increase the motivation to crib. McGreevy and colleagues found a “rebound” effect where cribbers who were prevented from cribbing with a collar significantly increased their cribbing activity when the collar was removed.

Ultimately, preventing a horse from performing the very behaviour that may alleviate his psychological or physical distress in an uncontrollable and adverse environment may be one of the most egregious, albeit inadvertent, cruelties. For confirmed, chronic cribbers a practical, humane and realistic solution is to provide them with a place where they can crib safely without destroying their surroundings. A metal u-shaped bar, fitted with PVC piping, that reduces tooth wear and stall damage, provides a very satisfactory cribbing station for a committed cribber.

In Conclusion

If, after you have implemented all the best management practices and your horse’s stereotypy continues with the same ferocity as ever, do not interpret a failure to eliminate or reduce an established stereotypy as a failure to improve welfare. Improving the horse’s environment may still significantly improve his psychological and physical well-being, despite not translating into a reduction in the intensity of the stereotypy. Remember, that as stereotypies move into “central control” the behaviour itself becomes reinforcing and occurs independently from the conditions that initially precipitated it. Take heart in the advice of equine researcher, Louise Nichols, who commented, “The goal is not to force them to stop, but to find ways to make them need it less.”