Sharon Smith MSc SEBC(Reg) IEng BHSAPC discusses the causes of stereotypical behaviour in horses and the best way to manage them.
Stable vices or, more correctly, stereotypical behaviours or ‘repetitive abnormal behaviours’, are a source of worry for many horse owners because it devalues the animal and can cause physical harm and unsightly muscle development over time.
Common stereotypical behaviours can be split into two types:
1) Stereotypical ‘compulsive disorder’ eg. most weaving; box-walking; pacing; head-tossing; self-mutilation. Compulsive disorders vary according to environment, and seem to increase anxiety and stress . These behaviours have an inappropriately directed goal but are not learned, as the behaviour is never reinforced. Weaving, for example, achieves a physical sensation like walking somewhat, but the horse has never achieved the real goal of walking forwards or relieving frustration. Compulsive disorders tend to develop after early infancy.
2) Repeated motor-pattern ‘stereotypy’ eg. crib-biting; wind-sucking; door-licking, or aimless rocking/weaving are strictly repetitive muscle movements that are unvarying and goalless, other than perhaps to self-comfort. Performing the behaviour seems to lower stress. They tend to arise in very early life.
Repetitive behaviours that are reinforced and goal-directed, are not stereotypies. For example, ‘Door-banging’ (repeatedly kicking the stable door) is rewarded by attention - the horse goal - even if they are shouted at. It can be de-trained without equipment, but everyone must consistently stop paying attention to the horse when they door-kick.
When looking at why stereotypical behaviours start, recent work suggests a genetic mutation located on the same DRD1 dopamine receptor gene as that for ‘elite sports performance’ . However, genetic tendency doesn’t mean the horse will develop an unwanted stereotypy. We have long known ‘nature’ and ‘nurture’ are not exclusive, and stereotypy has never been observed in feral horses. On closer inspection, both stereotypical behaviour and learning happen in a region of the brain called the striatum. The striatum in a horse resembles that of a human more so than apes, dogs… in fact perhaps any other animal we’ve studied! This similarity allows for some cross-species comparison . For example, we can learn more about crib-biting in horses by studying human stereotypy, such as ‘rocking’ or Tourette’s syndrome, and independent horse behaviour research tends to concur with findings in humans.
The main equine stereotypy triggers, ie. early life stress, pain, and lack of forage in the diet, are largely avoidable. Weaning can be carried out more gradually at a more appropriate age, using a ‘foster’ social group for increasing periods away from their dam, so the foal never feels isolated . A lack of forage in the diet causes stress and painful gastric ulcers . The Haygain Forager reduces stress while prolonging the intake of forage, compared with small-holed haynets .
In the event the horse develops a stereotypy, attempted ‘cures’ have been attempted with physical prevention and, when that fails, isolation - in case other horses copy the behaviour. We have now established that stereotypical behaviour isn’t learned – any more than thumb-sucking - so it cannot be copied. Aside from the immediate welfare implications, both prevention and isolation cause stress  and the horse may then modify the stereotypical behaviour or develop new ones. Anti-weaving door bars encourage stable-weaving or box-walking. Cribbing increases once anti-cribbing collars are removed . Chilli-pastes may result in the horse finding they can wind-suck on nothing at all. However, it is possible to reduce stereotypical behaviours in effective and humane ways:
Reducing the time spent engaged in stereotypical behaviours, through feeding forage and management changes, will reduce the likelihood of physical harm. But, if still worried, owners should facilitate safe performance of the behaviour. For example, covering a preferred cribbing surface with plastic pipe or rubber sheeting will protect front teeth, and rubber floor matting cushions legs from weaving.
There is a positive side to owning a horse prone to stereotypical behaviour. Evidence suggests they develop habits – responding automatically to new stimuli - faster than non-stereotypical horses  ie. they’ll consistently respond to aids sooner. Crib-biters, specifically, then find it difficult to un-learn tasks or modify their responses / movement . This tendency can be a mixed blessing, depending on your skill as a trainer or rider! They will continue to do exactly what they have learned, long after any reinforcement is withdrawn – ‘right’ or ‘wrong’! .
In summary: Stereotypies are avoidable through high welfare management and low-stress weaning. They can’t be un-learned or copied (because they aren’t ‘learned’), but can be minimised by reducing stress and prolonging forage intake. Traditional physical prevention is ineffective and isolation is unhelpful and completely unnecessary.
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