Equine Dental Vets

Stereotypies

A stereotypy is defined as a repeated movement with no obvious function either induced by frustration or brain dysfunction.

It is the name given to a group of behaviours which are commonly referred to as 'stable vices', however, the term 'vice' should not be used as it implies that there is something morally wrong with the horse. These repetitive behaviours can be seen commonly in zoo animals which pace up and down the fence or caged birds which pluck out their own feathers.

What are they?

Stereotypies are abnormal behaviours and rarely occur in animals living in their natural environment. Lack of companions, unnatural feeding and inability to make normal movements and exercise all increase the likelihood stereotypies will be shown.

Stereotypies must therefore be considered as behavioural problems which are a result of trying to cope with a problem.

One study found that around 15% of thoroughbred racehorses have stereotypies. In another study of 1750 horses, stereotypies were more common in dressage and event horses and were also more common in horses that spent more time stabled.

Wind-sucking or 'aero-phagia' involves the horse opening its mouth, contracting the pharyngeal musculature (muscles of the throat), flexing the neck muscles and sucking air into the proximal oesophagus, usually with a characteristic 'grunting' sound.

When a horse is crib-biting this action is accompanied by gripping with, or resting, the upper incisor teeth on a solid object such as a stable door or fence post. Once acquired, the behaviour is extremely persistent and can occur in environments very different to where it first arose. E.g. a horse that started wind-sucking in the stable may also start to do it in the paddock.

Do they affect the horse's health?

All stereotypies have an energy cost which may be high enough to result in weight loss in some circumstances. Some horses may choose to spend a reduced amount of time eating in order to crib-bite or wind-suck, and this can also result in weight loss. (see fig 2.)

Reports suggest a link between wind-sucking and spasmodic colic, this hasn't been proven although an association has been made with a type of colic where the small intestine becomes trapped in a space in the abdomen called the epiploic foramen.

The majority of the time there are no perceived adverse effects of stereotypic behaviours.

A man made problem

Evidence suggests horses have been crib-biting and windsucking since their domestication 15-30,000 years ago and the first written record of stereotypies appeared in a French text in 1609. Stereotypies are therefore thought to be a result of domestication and changes in the way the horse is kept.

The horse is designed to spend over 50% of its day grazing and in the wild will live in large open spaces in stable social groups. The consequences of stabling brings about a lack of social contact, restriction from normal movement and 'idleness' because of the use of cereal-based concentrates instead of forage, thereby reducing feeding time and feeding behaviour.

Studies have shown each of these factors bring about an increase in the likelihood of a horse performing a stereotypy.

If animals that show stereotypies are put into improved conditions they usually show a reduction in occurrence of the stereotypy.

Studies have also identified weaning as a critical point in development of oral stereotypies; two thirds of wind-suckers and crib-biters start within one month of weaning, at the same time as diet and environment are substantially altered.

Causes and motivation

Owners of horses that are established wind-suckers or crib-biters often notice the behaviour is displayed immediately after eating. Palatable, high cereal feeds can cause an increase in the acidity of the stomach and it has been speculated that increased acidity and abdominal discomfort are a trigger for crib-biting/wind-sucking behaviours. Production of alkaline saliva when wind-sucking may help the horse to neutralise stomach acid and therefore reduce discomfort. In addition some studies have found antacids as well as acting to decrease gastrointestinal inflammation and ulceration reduce the wind-sucking behaviour.

An alternative explanation for stereotypic behaviour in horses relates to stress-induced alterations in central nervous system (brain) dopamine physiology.

Dopamine is a neurotransmitter; a type of chemical released during stereotypic behaviour that helps control the pleasure and reward centres in the brain. Horses that wind-suck have been found to have significantly higher numbers of dopamine receptors in the area of the brain that controls goal-directed behaviours associated with attaining rewards and avoiding negative stimulus.

If the animals' environment doesn't allow it to attain goals (movement, socialising, feeding) the animal is maintained in a heightened state of goal-attainment. It is this 'appetite phase' of goal attainment that is the basis for stereotypy development.

Chronic stress caused by restricted feeding, restricted exercise and social isolation is the most likely cause for development of equine stereotypies. In particular stress early in development may be critical, particularly management at weaning.

As with other species (in particular humans) some forms of brain damage could potentially be a cause of stereotypies in the horse. However this is rarely, if ever, the cause of the stereotypies that we commonly see.

Stereotypies are not 'contagious'

Owners often regard wind-sucking as 'contagious', believing other horses will copy the behaviour. As such, these horses are often confined away from other animals on the property because their monetary value is usually less than a similar animal free of any stereotypies. However there is no evidence to support this. Development of stereotypies does not normally occur at pasture, and it is unlikely that wind-sucking behaviour would be copied in these circumstances.

When stabled horses show stereotypies (see fig 3.) they must have frustrations over their environment, whether or not they have initiated that behaviour by copying others. Equally the idea that there is a genetic component to stereotypies is unproven. It is likely this idea stems from related horses being kept in similar housing and management conditions.

Can horses be cured?

Various methods to prevent wind-sucking and crib-biting have been tested. A crib-strap or cribbing collar consisting of a strap around the ears and neck with either protruding leather or two pieces of jointed steel hinged together at the throat. The collar works by tightening around the pharynx as the horse attempts to arch its neck. These collars don't work for every horse and in one study horses prevented from crib-biting with a collar for 24 hours resumed the behaviour at a higher rate than before when the collars were removed. (see fig 1.)

The horses also seem to adapt to the collars, which then require continued tightening and can result in skin trauma. Aversion therapy has also been attempted with electric shock collars, despite promising early reports only 9 horses out of 60 were 'cured' and 3 of these had required reinforcement therapy after 9 months.

Surgical interventions

Three surgical methods to prevent wind-sucking have been described. The first is a neurectomy which involves removal of the surrounding nerve tissue of the sternomandibularis muscle of the neck. The second is a myectomy, which involves the removal of omohyoid and sternohyoideus neck muscles. These surgeries work by preventing sufficient arching of the neck but are not always successful and can cause severe frustration to the horse as they are then unable to carry out certain movements. The last surgery is a buccostomy and involves making a hole through the horses cheek into its mouth, the idea is that the horse requires a 'seal' to suck in air. This surgery often doesn't work, causes disfigurement and regularly heals over anyway.

Both surgery and collars in an attempt to reduce the occurrence of wind-sucking and crib-biting result directly in poorer horse welfare and do not lead to permanent improvement even if welfare is ignored so they should be discouraged.

Enrichment

Hanging stable-toys, balls and licks to reduce "boredom" in the horse are often sold to owners to reduce stereotypies, however there is very little evidence to suggest they reduce 'boredom' and the stereotypic behaviour that supposedly results from it. However devices that stimulate natural foraging behaviours, like the ones that release small amounts of food as the animal spends time pushing them around the stable can help to reduce the time spent performing stereotypic behaviours.

Drug treatments

Transient elimination of crib-biting has been reported in subjects treated with naloxone, nalmefene or diprenorphine, these are drugs used to treat alcohol and drug addictions in humans. These work in the brain to reduce the heightened state of 'goal-attainment' discussed earlier. The study used nalmefene in a continuous infusion for 1 week and for that week no cribbing was observed. However daily injections would be expensive and are not practical and the behaviour returns when the drug is stopped.

Prevention better than cure

As in other species the presence of stereotypies in horses indicates poor welfare, usually due to inadequacies in management. Attempts to prevent it with collars that restrict neck movements or by severing muscles and nerves surgically will have no beneficial effect on the horse's real problem. In fact it will cause additional frustration for the animal and potentially unnecessary pain and suffering.

Stereotypies — Management Strategies

It is the causes (motivation) of wind-sucking/crib-biting rather than the action that should be treated.

1 Let them do it Remember that stereotypies are a coping mechanism so unless the horse is injuring himself or is at high risk of colic he is unlikely to benefit from attempts to block the stereotypy and horse welfare should be the primary consideration. If you have a crib-biter provide him with a non-abrasive surface they can bite (e.g. cover a rail with rubber) and discourage him from biting other surfaces (e.g. with electric tape or a taste deterrent).

2 Improved housing Long-term the goal should be to improve housing and management. Housing should provide opportunity for movement and a variety of stimulation. The horse should have adequate space to exercise, ideally where they are kept or an area they can access daily for intervals.

3 Social contact should be maximised preferably by being kept in groups or with a companion and being able to touch and see other horses when stabled.

4 Nutrition should be adequate and quality forage that takes a long time to collect and eat should be provided. Restrictor haynets (slow feeding haynets) are a great way to keep the horse busy for longer periods, however having to work harder may frustrate some horses which could become an additional stressor.

5 Other strategies of reducing the behaviour involve altering dopamine transmission, this can be achieved with drugs like nalmefene or without drugs through ad libitum feeding, increasing periods of turn out and socialisation and also with acupuncture. Interestingly acupuncture which reduces dopaminergic activity in the brain has been shown to reduce crib-biting and wind-sucking in some horses.


Chew on this

Radiography of horses as they were crib-biting challenges the traditional view that crib-biters actually swallow air, because there was no movement of the tongue as one would expect in true swallowing.

Instead, each horse showed an explosive distension of the proximal esophagus that prompted no peristalsis (the wavelike muscular contractions that go with swallowing). Much of the air exited the proximal esophagus between crib-bites by returning through the cranial esophageal sphincter into the pharynx (the air exited out of the open mouth). This may explain why tympanitic colic (abdominal pain associated with wind or flatulence) is not seen in all crib-biting horses.

On the right is a composite image from three stills captured during fluoroscopy of the cranial half of a horse's neck during a bout of crib-biting. Air is visible in the esophagus (E), trachea (T) and oropharynx (Or). (see fig. 5) Reproduced with permission from Equine Behaviour, A Guide for Veterinarians and Equine Scientists by Paul McGreevy)


CRIB-BITER or WIND-SUCKER?

A crib-biter repeatedly seizes fixed objects with its incisor teeth and pulls back while making a characteristic grunting noise that signifies the passage of air into the esophagus. A wind-sucker achieves the same characteristic neck posture and grunt without holding onto any fixed object. It is believed that crib-biters may become wind-suckers – for example, if no substrate is available, or if this component of the behavior is punished. Horses that merely hold onto a fixed object without grunting are said to show grasping.


Wind-sucking and crib-biting horses require expert dental care (see fig. 4)

Because horses that wind-suck or crib-bite spend many hours a day using their mouths, often on highly abrasive surfaces like timber or metal, it is not uncommon for them to excessively wear their front teeth. When this type of rapid wear occurs, the nerve and blood supply to the tooth can be exposed. This often results in the death of these structures and can lead to bacterial infection of the tooth roots.

If you have a horse who wind-sucks or crib-bites then regular dental exams from a dental vet are an important part of their care. You can find a dental vet in your area of Australia using the dedicated search on this website — click here.

Take Home Message

So far a cure for stereotypic behaviours remains elusive. Instead of concentrating on prevention we should be working to avoid the development of stereotypies by improving the welfare, housing and management of our horses from weaning to retirement.

Stereotypies

Stereotypies

A stereotypy is defined as a repeated movement with no obvious function either induced by frustration or brain dysfunction.

It is the name given to a group of behaviours which are commonly referred to as 'stable vices', however, the term 'vice' should not be used as it implies that there is something morally wrong with the horse. These repetitive behaviours can be seen commonly in zoo animals which pace up and down the fence or caged birds which pluck out their own feathers.

What are they?

Stereotypies are abnormal behaviours and rarely occur in animals living in their natural environment. Lack of companions, unnatural feeding and inability to make normal movements and exercise all increase the likelihood stereotypies will be shown.

Stereotypies must therefore be considered as behavioural problems which are a result of trying to cope with a problem.

One study found that around 15% of thoroughbred racehorses have stereotypies. In another study of 1750 horses, stereotypies were more common in dressage and event horses and were also more common in horses that spent more time stabled.

Wind-sucking or 'aero-phagia' involves the horse opening its mouth, contracting the pharyngeal musculature (muscles of the throat), flexing the neck muscles and sucking air into the proximal oesophagus, usually with a characteristic 'grunting' sound.

When a horse is crib-biting this action is accompanied by gripping with, or resting, the upper incisor teeth on a solid object such as a stable door or fence post. Once acquired, the behaviour is extremely persistent and can occur in environments very different to where it first arose. E.g. a horse that started wind-sucking in the stable may also start to do it in the paddock.

Do they affect the horse's health?

All stereotypies have an energy cost which may be high enough to result in weight loss in some circumstances. Some horses may choose to spend a reduced amount of time eating in order to crib-bite or wind-suck, and this can also result in weight loss. (see fig 2.)

Reports suggest a link between wind-sucking and spasmodic colic, this hasn't been proven although an association has been made with a type of colic where the small intestine becomes trapped in a space in the abdomen called the epiploic foramen.

The majority of the time there are no perceived adverse effects of stereotypic behaviours.

A man made problem

Evidence suggests horses have been crib-biting and windsucking since their domestication 15-30,000 years ago and the first written record of stereotypies appeared in a French text in 1609. Stereotypies are therefore thought to be a result of domestication and changes in the way the horse is kept.

The horse is designed to spend over 50% of its day grazing and in the wild will live in large open spaces in stable social groups. The consequences of stabling brings about a lack of social contact, restriction from normal movement and 'idleness' because of the use of cereal-based concentrates instead of forage, thereby reducing feeding time and feeding behaviour.

Studies have shown each of these factors bring about an increase in the likelihood of a horse performing a stereotypy.

If animals that show stereotypies are put into improved conditions they usually show a reduction in occurrence of the stereotypy.

Studies have also identified weaning as a critical point in development of oral stereotypies; two thirds of wind-suckers and crib-biters start within one month of weaning, at the same time as diet and environment are substantially altered.

Causes and motivation

Owners of horses that are established wind-suckers or crib-biters often notice the behaviour is displayed immediately after eating. Palatable, high cereal feeds can cause an increase in the acidity of the stomach and it has been speculated that increased acidity and abdominal discomfort are a trigger for crib-biting/wind-sucking behaviours. Production of alkaline saliva when wind-sucking may help the horse to neutralise stomach acid and therefore reduce discomfort. In addition some studies have found antacids as well as acting to decrease gastrointestinal inflammation and ulceration reduce the wind-sucking behaviour.

An alternative explanation for stereotypic behaviour in horses relates to stress-induced alterations in central nervous system (brain) dopamine physiology.

Dopamine is a neurotransmitter; a type of chemical released during stereotypic behaviour that helps control the pleasure and reward centres in the brain. Horses that wind-suck have been found to have significantly higher numbers of dopamine receptors in the area of the brain that controls goal-directed behaviours associated with attaining rewards and avoiding negative stimulus.

If the animals' environment doesn't allow it to attain goals (movement, socialising, feeding) the animal is maintained in a heightened state of goal-attainment. It is this 'appetite phase' of goal attainment that is the basis for stereotypy development.

Chronic stress caused by restricted feeding, restricted exercise and social isolation is the most likely cause for development of equine stereotypies. In particular stress early in development may be critical, particularly management at weaning.

As with other species (in particular humans) some forms of brain damage could potentially be a cause of stereotypies in the horse. However this is rarely, if ever, the cause of the stereotypies that we commonly see.

Stereotypies are not 'contagious'

Owners often regard wind-sucking as 'contagious', believing other horses will copy the behaviour. As such, these horses are often confined away from other animals on the property because their monetary value is usually less than a similar animal free of any stereotypies. However there is no evidence to support this. Development of stereotypies does not normally occur at pasture, and it is unlikely that wind-sucking behaviour would be copied in these circumstances.

When stabled horses show stereotypies (see fig 3.) they must have frustrations over their environment, whether or not they have initiated that behaviour by copying others. Equally the idea that there is a genetic component to stereotypies is unproven. It is likely this idea stems from related horses being kept in similar housing and management conditions.

Can horses be cured?

Various methods to prevent wind-sucking and crib-biting have been tested. A crib-strap or cribbing collar consisting of a strap around the ears and neck with either protruding leather or two pieces of jointed steel hinged together at the throat. The collar works by tightening around the pharynx as the horse attempts to arch its neck. These collars don't work for every horse and in one study horses prevented from crib-biting with a collar for 24 hours resumed the behaviour at a higher rate than before when the collars were removed. (see fig 1.)

The horses also seem to adapt to the collars, which then require continued tightening and can result in skin trauma. Aversion therapy has also been attempted with electric shock collars, despite promising early reports only 9 horses out of 60 were 'cured' and 3 of these had required reinforcement therapy after 9 months.

Surgical interventions

Three surgical methods to prevent wind-sucking have been described. The first is a neurectomy which involves removal of the surrounding nerve tissue of the sternomandibularis muscle of the neck. The second is a myectomy, which involves the removal of omohyoid and sternohyoideus neck muscles. These surgeries work by preventing sufficient arching of the neck but are not always successful and can cause severe frustration to the horse as they are then unable to carry out certain movements. The last surgery is a buccostomy and involves making a hole through the horses cheek into its mouth, the idea is that the horse requires a 'seal' to suck in air. This surgery often doesn't work, causes disfigurement and regularly heals over anyway.

Both surgery and collars in an attempt to reduce the occurrence of wind-sucking and crib-biting result directly in poorer horse welfare and do not lead to permanent improvement even if welfare is ignored so they should be discouraged.

Enrichment

Hanging stable-toys, balls and licks to reduce "boredom" in the horse are often sold to owners to reduce stereotypies, however there is very little evidence to suggest they reduce 'boredom' and the stereotypic behaviour that supposedly results from it. However devices that stimulate natural foraging behaviours, like the ones that release small amounts of food as the animal spends time pushing them around the stable can help to reduce the time spent performing stereotypic behaviours.

Drug treatments

Transient elimination of crib-biting has been reported in subjects treated with naloxone, nalmefene or diprenorphine, these are drugs used to treat alcohol and drug addictions in humans. These work in the brain to reduce the heightened state of 'goal-attainment' discussed earlier. The study used nalmefene in a continuous infusion for 1 week and for that week no cribbing was observed. However daily injections would be expensive and are not practical and the behaviour returns when the drug is stopped.

Prevention better than cure

As in other species the presence of stereotypies in horses indicates poor welfare, usually due to inadequacies in management. Attempts to prevent it with collars that restrict neck movements or by severing muscles and nerves surgically will have no beneficial effect on the horse's real problem. In fact it will cause additional frustration for the animal and potentially unnecessary pain and suffering.

Stereotypies — Management Strategies

It is the causes (motivation) of wind-sucking/crib-biting rather than the action that should be treated.

1 Let them do it Remember that stereotypies are a coping mechanism so unless the horse is injuring himself or is at high risk of colic he is unlikely to benefit from attempts to block the stereotypy and horse welfare should be the primary consideration. If you have a crib-biter provide him with a non-abrasive surface they can bite (e.g. cover a rail with rubber) and discourage him from biting other surfaces (e.g. with electric tape or a taste deterrent).

2 Improved housing Long-term the goal should be to improve housing and management. Housing should provide opportunity for movement and a variety of stimulation. The horse should have adequate space to exercise, ideally where they are kept or an area they can access daily for intervals.

3 Social contact should be maximised preferably by being kept in groups or with a companion and being able to touch and see other horses when stabled.

4 Nutrition should be adequate and quality forage that takes a long time to collect and eat should be provided. Restrictor haynets (slow feeding haynets) are a great way to keep the horse busy for longer periods, however having to work harder may frustrate some horses which could become an additional stressor.

5 Other strategies of reducing the behaviour involve altering dopamine transmission, this can be achieved with drugs like nalmefene or without drugs through ad libitum feeding, increasing periods of turn out and socialisation and also with acupuncture. Interestingly acupuncture which reduces dopaminergic activity in the brain has been shown to reduce crib-biting and wind-sucking in some horses.


Chew on this

Radiography of horses as they were crib-biting challenges the traditional view that crib-biters actually swallow air, because there was no movement of the tongue as one would expect in true swallowing.

Instead, each horse showed an explosive distension of the proximal esophagus that prompted no peristalsis (the wavelike muscular contractions that go with swallowing). Much of the air exited the proximal esophagus between crib-bites by returning through the cranial esophageal sphincter into the pharynx (the air exited out of the open mouth). This may explain why tympanitic colic (abdominal pain associated with wind or flatulence) is not seen in all crib-biting horses.

On the right is a composite image from three stills captured during fluoroscopy of the cranial half of a horse's neck during a bout of crib-biting. Air is visible in the esophagus (E), trachea (T) and oropharynx (Or). (see fig. 5) Reproduced with permission from Equine Behaviour, A Guide for Veterinarians and Equine Scientists by Paul McGreevy)


CRIB-BITER or WIND-SUCKER?

A crib-biter repeatedly seizes fixed objects with its incisor teeth and pulls back while making a characteristic grunting noise that signifies the passage of air into the esophagus. A wind-sucker achieves the same characteristic neck posture and grunt without holding onto any fixed object. It is believed that crib-biters may become wind-suckers – for example, if no substrate is available, or if this component of the behavior is punished. Horses that merely hold onto a fixed object without grunting are said to show grasping.


Wind-sucking and crib-biting horses require expert dental care (see fig. 4)

Because horses that wind-suck or crib-bite spend many hours a day using their mouths, often on highly abrasive surfaces like timber or metal, it is not uncommon for them to excessively wear their front teeth. When this type of rapid wear occurs, the nerve and blood supply to the tooth can be exposed. This often results in the death of these structures and can lead to bacterial infection of the tooth roots.

If you have a horse who wind-sucks or crib-bites then regular dental exams from a dental vet are an important part of their care. You can find a dental vet in your area of Australia using the dedicated search on this website — click here.

Take Home Message

So far a cure for stereotypic behaviours remains elusive. Instead of concentrating on prevention we should be working to avoid the development of stereotypies by improving the welfare, housing and management of our horses from weaning to retirement.

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