Equine stereotypic behaviours are repetitive behaviours involving a constant sequence of movements that have no obvious or apparent function. 
Examples of common stereotypies include cribbing, wind-sucking, weaving, stall walking and head shaking. Sometimes referred to as stall vices, these behaviours are estimated to affect 10-20% of domesticated horses.
These abnormal behaviours may emerge as a response to stress, confinement, isolation or other sources of discomfort for your horse. While the exact cause of stereotypies is not well understood, they appear to be coping mechanisms or expressions of frustration.
Correctly diagnosing abnormal equine behaviour and understanding what it means is an important skill for every horse owner. In the past, it was not uncommon to dismiss behavioural abnormalities due to a lack of understanding. Only recently has stereotypic behaviour received significant attention from the scientific community.
Once you have identified a stereotypic behaviour in your horse, you can take steps to address the root cause of the behaviour. Improving your horse’s overall welfare through care, feeding and management practices is the best way to prevent stereotypies from occurring.
What is Stereotypic Behaviour?
Stereotypic behaviours in horses are defined as, “stylized, repetitive, apparently functionless motor responses or sequences.”  It is hypothesized that these behaviours are designed to reduce stress in the animal.
There is not a clearly defined categorization of stereotypies. For example, identification criteria are subjective and it can be difficult to distinguish a behaviour that is functional versus functionless.
Behaviours described by some researchers and behaviourists as stereotypic are classed differently by others. 
However, these behaviours are generally divided into two categories:
- Locomotor stereotypies involving movement
- Oral stereotypies involving the mouth
Sometimes, there is a clear cause of the behaviour related to the horse’s environment or routine. The behaviour may appear on a regular or predictable schedule. Other times, the behaviour may appear sporadically or unprovoked.
Some horses may display these behaviours intermittently, while others persist in the activity for long periods of time and devote considerable effort towards it. 
Horses that exhibit these behaviours may be otherwise healthy and able to be ridden. On the other hand, some horses with stereotypies are unrideable, have anxious temperaments or other health problems.
They may also develop related issues such as poor appetite, weight loss or poor performance as a result of increased energy expenditure or disruption to normal feeding and foraging. 
These behaviours can be a minor nuisance to horse owners, but they can also lead to long-term physiological problems depending on the severity and the behaviour exhibited.
Stereotypies may be referred to as “unsoundness” by horse owners conducting pre-purchase exams, thus reducing the value of the horse.
This article aims to help you identify common stereotypic behaviours in horses and learn about the concerns associated with these behaviours.
Functionless vs Conditioned Behaviours
Stereotypic behaviours lack function meaning that there is no beneficial consequence to the horse. These behaviours are purposeless. 
It is often difficult to ascertain whether a repetitive behaviour is stereotypic because some unique and abnormal behaviours do have a purpose.
For example, pawing and kicking may be repetitive, but operantly conditioned and not stereotypic. A horse may paw or kick at feeding time if it can see its food to receive more immediate attention from the caregiver.
The horse is fed after performing this behaviour, which results in positive reinforcement. 
In this case, pawing and kicking are not a stereotypical behaviour, as they have been learned and reinforced by feeding.
Displacement Behaviours vs. Stereotypic Behaviours:
Another important distinction is between displacement behaviours and stereotypies. Displacement behaviours are behaviour patterns characterized by an inappropriate or irrelevant reaction to a given situation. 
Self-grooming in an inappropriate situation is an example of a displacement behaviour. These behaviours are often immediate responses to a stressful situation.
If an abnormal behaviour appears during a stressful or unique situation, it is most likely a displacement behaviour. In contrast, stereotypies develop over longer periods of time. 
Displacement activities may appear in unusual contexts but typically subside as the stressful environmental conditions or stimuli resolve. 
The context of the behaviour is important. Inappropriate self-grooming is considered a displacement behaviour in stressful situations but would be classified as stereotypic behaviour (self-mutilation) if it occurred on a repetitive, perpetual, rhythmic basis in a stalled horse. 
Vices vs. Stereotypies:
Historically, stereotypies were referred to as stall or stable vices.  The use of the phrase vice is now viewed as incorrect because it suggests that something is morally wrong with the horse performing these behaviours.
This is an anthropomorphic concept, involving the attribution of human traits, emotions and intentions onto horses. Using the word “vice” implies that the horse is choosing to act in this manner and wouldn’t exhibit these behaviours if it had more willpower.
Stereotypic behaviour is usually an automated coping response for a horse in a non-species appropriate environment. The expression of these behaviours is out of the horse’s control. 
Risk Factors for Stereotypies
Stereotypic behaviour is believed to develop in response to a frustrating environment. Feeding practices, stable conditions, weaning methods and other management factors have been studied for their role in contributing to these behaviours. 
Between 10-40% of stabled horses experience stereotypic behaviours. In comparison, these behaviours are rarely observed in wild or free-ranging horses. 
Stereotypies are also reported to be more common in racehorses. There may also be genetic or neurological factors that contribute to the performance of stereotypic behaviour. 
Housing horses together with horses that are displaying stereotypies can result in copying or mimicry of the stereotype. For this reason, many horse owners avoid housing stereotypic and non-stereotypic horses together.
This may lead to isolation of the stereotypic horses, potentially exacerbating the behavior. 
It is not uncommon to see conflicting information regarding what is classified as a stereotypy.
Some colloquial names for stereotypic behaviours include “chewing, lip-licking, licking environment, wood-chewing, crib-biting, windsucking, stall-walking, weaving, pawing, tail-swishing, door kicking (front foot), door kicking (back foot), rubbing, self-biting, head-tossing, head-circling, head-shaking, head-nodding, head extending, [and] kicking stall.”
We will divide these behaviours into eight broad categories below: 
- Cribbing / Windsucking
- Box (Stall) Walking / Pacing
- Wood Chewing
- Self Mutilation (including stall kicking)
- Stereotypic Licking (and other oral behaviours)
- Stereotypic Head Movements
Individual stereotypies present their own inherent risks for the animal, which are addressed below.
Some behaviours are commonly displayed in conjunction with others, and it is not uncommon to see a horse with more than one stereotypic behaviour.
#1: Cribbing / Windsucking:
Crib biting or “cribbing” is an oral stereotypic behaviour. A horse grips onto a fixed object, usually around chest level, with its incisor teeth.
The horse will lean back on its hindquarters, contract the muscles on its neck, and bring its head into an arched position. Air is drawn into the cranial esophagus, producing a grunting sound.
Cribbing occurs on a variety of solid surfaces. A horse may even crib on barbed wire or electric fencing if no other surfaces are available. 
Windsucking, which is less common than cribbing, displays the same characteristics without holding onto a fixed object.
Crib-biters may become windsuckers if there are no available surfaces for them to crib on or if the grasping behaviour is punished. 
Both cribbing and windsucking involve a quick intake of breath often accompanied by a grunting noise. This behaviour is sometimes referred to as aerophagia, but little to no air is actually swallowed. 
Horses that crib will often have clear erosion on the incisor teeth and pronounced hypertrophy (increase in muscle growth) of the neck muscles.
Cribbing has also been linked to weight loss and poor body condition. This may be connected to the amount of energy required to repeatedly crib-bite and to reduced time spent foraging, eating and grazing. 
There is also a correlation between cribbing and temporohyoid osteoarthritis (THO). THO is a progressive disease of the temporohyoid joint, characterized by excess bone growth and decreased range of motion. 
Another concern for horse owners is environmental damage caused by cribbing behaviour. Fences, buckets and ledges may become damaged if the horse grips them with its teeth.
Weaving is a locomotive stereotypic behaviour that involves lateral movement of the neck and head from side to side. It is a repetitive motion in which the horse alternates its weight between forelegs. 
Weaving typically occurs with the horse’s head over a stable door but can be observed in other locations. 
The horse may average 30-90 repetitions of weaving behaviour per minute and may weave for up to 3 hours a day. 
Weaving can lead to orthopedic problems such as strained ligaments, loss of body condition and poor performance. 
Horses that weave will have more wear on their feet. For horses that are shoed, the shoe will be worn down and need to be replaced sooner. 
#3: Stall Walking or Pacing:
A horse who Stall Walks or Box Walks will repeatedly walk around the stall in a circle.  The size of the stall does not affect the behaviour. Horses that are given a larger area will often circle in one corner.
Restraining a horse that stall walks or preventing the circular walking pattern will likely result in the expression of weaving behaviour.
Some horses will circle for hours a day, at a rate of several repetitions per minute (depending on the stall size).  Stereotypic stall walking patterns are unique from horse to horse. Some horses will circle over and over in one direction while others will form specific and consistent patterns within the stall. 
Pacing refers to stereotypic movement along a barrier, usually at a walk or trot. Horses that pace may also move in a figure 8 pattern between parts of the enclosure; these turns will occur at a specific and consistent location.
Horses that pace in a straight line will often turn when they reach a barrier and change direction.  The consistent pacing may result in a trench along the fence or near the gate.
Most horses will periodically circle in their stall or pace down a fence or at a gate, especially when it is time for feeding. Pacing and circling are only considered stereotypic behaviours if they become excessive and replace other activities such as eating, foraging or resting. 
Horses that circle or pace constantly may begin to lose body condition and lose weight as their walking expends more energy than they consume. 
This stereotypy may become excessive to the point that the horse expresses this behaviour to the exclusion of normal activities including eating and drinking.
Depending on the pattern size of the circling, there is sometimes continuous (and uneven) flexion on the spine.  Studies have indicated that this repetitive motion predisposes a horse to rhabdomyolysis – a potentially life-threatening syndrome that is a result of the breakdown of skeletal muscle fibres. 
#4 Wood Chewing:
Similar to cribbing, wood-chewing horses will grasp a horizontal surface like a fence board with their teeth. Unlike cribbing, the horse will actually ingest the wood. 
Wood chewing may be stereotypic or it may reflect a need to satisfy nutritional requirements or to express species-appropriate foraging behaviours. Once nutritional needs are met, wood-chewing may cease immediately. 
Wood is a normal component of a wild horse’s diet. Wood provides extra fibre and nutrients and may be used as self-medication because some plants often contain medical properties. 
When evaluating wood-chewing behaviour, the first step is to assess the dry matter and fibre content of the horse’s diet. Is the horse going long periods of time between meals or spending intermittent periods with an empty stomach?
If proper roughage is provided and the horse does not have long periods between feedings, then the behaviour is purposeless and genuinely stereotypic. In this case, the horse’s motivation to chew may be reduced but it may be difficult to eliminate. 
Similar to cribbing, wood-chewing can cause extreme wear on your horse’s teeth. Digesting wood (especially treated wood) can cause gastrointestinal issues.
Additionally, the risk of splinters and the presence of nails also put the horse at risk of puncture and wounds in their mouth or esophagus. 
Wood-chewing stereotypic behaviour is a common problem in stabled environments and horses may chew up to 1 lb of unnatural or treated wood daily. It can be a costly problem as the horse may chew fence rails, door edges and parts of the barn which eventually need replacing. 
Pawing is the act of dragging a foot across the ground or motioning in the air. This is a normal behaviour that becomes a stereotypic behaviour when it is excessive.
Pawing must be observed and continued outside of feeding situations for it to be appropriately classified as a stereotypy. 
Pawing is considered a displacement activity that may have biologically originated from the activity of uncovering food in the snow.
Horses will normally paw in a variety of situations such as:
- When being restrained
- When eating grain
- In anticipation of food
- When not wanting to stand
- To reach other horses
- In response to pain
- When needing to escape
In all of these situations, the pawing behaviour has a function and would not be considered stereotypic. 
Compulsive pawing can result in the loosening or the removal of horseshoes and can damage the hooves.
Additionally, pawing can cause injury to both the horse and rider, can hinder training and can be a financial burden due to injury or farrier issues. 
#6 Self Mutilation (including stall kicking):
There are three categories of self-mutilation:
Type 1: A normal behavioural response to intermittent or persistent physical discomfort (allergies or pain).
Type 2: Found in stallions; self-directed inter-male aggression.
Type 3: A repetitive, invariant and often rhythmic behaviour causing self-mutilation. 
Type 1 and 2 behaviours are often sudden whereas Type 3 behaviours are generally subtle and take place on a predictable schedule or pattern. Type 3 behaviours include nipping at various parts of the body, stomping and kicking. 
Stereotypic stall kicking involves the repetitive striking of the stall walls with the horse’s hocks or hooves. This behaviour is not directed at a specific target.
In order for stall kicking to be classified as a stereotypic behaviour, it needs to have no clear motivation or external reinforcement. 
Self-mutilation can cause injury to your horse and in extreme cases may be life-threatening. 
#7 Stereotypic Licking (and other oral behaviours)
Repetitive licking of non-food items is an oral stereotypic behaviour. It sometimes involves the stable walls and floors or the sides of food buckets.
Licking is a natural function of the horse and is purpose-directed if the goal is to seek out additional nutrients in the environment. However, licking is classified as a stereotypic behaviour when it is focused on a single location and is repetitive.
Other oral stereotypic behaviours include sham-chewing or tooth-grinding. In these behaviours, the horse is repetitively performing tongue, mouth or jaw movements without any food in its mouth.
These behaviours are sometimes conducted in anticipation of feeding, in which case they are not stereotypic behaviours.
Behaviours such as tongue rolling and lip movements are also sometimes described as stereotypic, but these behaviours usually have a function and are unlikely to be true stereotypies. 
It is rare for these oral behaviours to be stereotypies as they are often identified as having a cause upon investigation. 
Licking is believed to be a stepping stone to the stereotypic behaviour of crib-biting. 
Behaviours such as lip-smacking, tongue playing and lolling are often ignored by owners outside of riding. However, during riding and within the show ring, these behaviours are not aesthetically pleasing and the horse may place its tongue over the bit causing problems. 
#8 Stereotypic head movements:
Abnormal head movements can have many causes; careful evaluation is warranted to eliminate possible explanations of the movement.
The majority of these head movements are not stereotypic behaviour; it is more common that they are accidentally conditioned movements.
Head nodding involves the vertical movement of the head and neck, typically above the stable door or other barriers. It involves repetitive precise head movements as opposed to wild or aggressive movements. 
Head shaking often implies that your horse is experiencing irritation in a specific spot. Horses may shake their head horizontally and may attempt to rub their ears. This is usually a pain response, such as a reaction to an ear mite infestation. 
Horses that exhibit head-shaking usually cannot compete or be safely ridden unless the behaviour resolves.
These behaviours are usually a response to pain and irritation or a behavioural problem.  Because head-shaking is not usually stereotypic, the behaviour may be easier to resolve through training and addressing the source of any discomfort.
For a behaviour to be classified as a stereotypic behaviour it needs to be functionless and repetitive. This is largely context-dependent and based on how the specific behaviour is performed.
It can be difficult to ascertain whether a behaviour lacks a purpose; some behaviours that are repetitive do have a function or result in some beneficial consequence to the horse.
For example, a behaviour that is repeated prior to feeding time will become positively reinforced and would not be considered stereotypic.
There are many different hypotheses for why horses exhibit stereotypic behaviour. They may result from a lack of stimulation or a sub-optimal environment that does not support a species-appropriate lifestyle.
Regardless of the cause, stereotypic behaviours are often sustained for long periods of time and can cause continuous strain on the animal.
They may result in injury, deterioration of the horse’s physical condition, or damage to the environment. Equine stereotypic behaviours are worth investigating with the help of a professional.
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