Crib-biting, wind-sucking and wood-chewing are repetitive oral behaviours that are most commonly seen in stabled horses. Crib-biting and wind-sucking are similar behaviours and may reflect digestive discomfort, whereas wood-chewing may simply reflect re-directed feeding behaviour. Nonetheless, all may be treated and prevented most effectively by providing the horse with natural grazing and increased forage.

Crib-biting describes a repetitive oral behaviour most commonly observed when the horse is stabled. The horse grasps the edge of a fixed object, e.g. the top of a stable door, between its incisor teeth and pulls backwards. They flex their neck muscles as they do so and may also make a characteristic ‘grunting’ noise. Crib-biting should not be confused with wood-chewing, but is often combined with wind-sucking.

Wind-sucking describes a similar behaviour to crib-biting; arching of the neck and engulfing of air into the oesophagus. However, in this case the horse does not grasp hold of a fixed object. Wind-sucking is thought to form part of the mechanism of crib-biting, rather than being defined as an entirely separate behaviour.

Wood-chewing describes the repetitive chewing of wood-based items within the horse’s vicinity, i.e. the top of the stable door and fences. The behaviour appears more ‘normal’ than crib-biting and wind-sucking and, although often persistent, may be more simply a re-direction of feeding activity, particularly when horses are fed low forage diets.

Crib-biting and wind-sucking may also be referred to as oral stereotypies.
Stereotypies are behaviours defined as ‘repetitive, relatively invariant sequences of behaviour with no obvious goal or function’. Wood-chewing may not be considered a stereotypy because there does appear to be a goal in this case (eating wood), however in some cases the behaviour may become so fixated that it might be considered to be a stereotypy.
Stereotypies occur in a wide range of species, usually when they are held in captivity. This leads researchers to suggest that it is the environment that is causing the problem. Although the exact mechanism for the formation of the behaviour is still not properly understood, they arise as a result of a combination of immediate and past environmental factors in a predisposed individual at a given time.
Stereotypies such as crib-biting, wind-sucking and wood-chewing have never been documented in feral horse populations, but are reported to occur in 15-37% of domestic horses. More specifically, up to 4.2% of domestic horses have been reported to engage in crib-biting alone. Again, this suggests that it may be the environment that is partly to blame.
These behaviours are considered problematic for a number of reasons, for example crib-biters may slowly wear away their front teeth, which might in extreme cases lead to problems with grazing. Other associated problems are thought to include:

  • weight loss
  • poor appetite
  • increased water intake
  • hypertrophy of ventral neck muscles
  • gastrointestinal problems, including gastric ulceration and colic.

The time your horse spends crib-biting and/or wind-sucking may also reduce the time spent feeding and resting. However recent research suggests that, contrary to popular belief, crib-biting does not involve the passage of air into the stomach; rather it is expelled again through the mouth. The grunting noise may therefore represent more of a burp than a gulp! There is also increasing evidence that crib-biting may reflect the same underlying cause of gastric problems such as ulcers and colic, rather than being the cause of them.

Crib-biting has been identified as a potential factor in the development of certain types of colic and gut ulceration but, as yet, it is not fully ascertained as to whether this stereotypy is a direct contributor to these disorders or an indicator of other management factors which impact upon the well-being of the horse. The current view in equine science is that it is liable to be the latter.
The development of abnormal oral behaviours can occur in foals prior to weaning but increases directly following weaning and may be related to stressful box weaning and the provision of concentrated feed. Comparative to those that do not, foals which develop abnormal oral behaviours after weaning spent more time suckling from the dam and twice as much time teat nuzzling. It is possible that thwarting of the feeding behaviours of the foal at weaning may directly contribute to the development of these oral stereotypies.
In a 4 year prospective study, Amanda Waters and her colleagues from Bristol University, UK, established the incidence of crib-biting to be 10.5% in horses by the median age of 20 weeks. It was also found that the provision of concentrates after weaning was responsible for increasing the incidence of crib-biting by a factor of 4 and that low provision of forage material also has a significant impact.

Both crib-biting and wind-sucking have repeatedly been associated with stabling and the provision of a highly concentrated diet with little forage. Such changes are often to be seen at weaning and are accompanied by other stressors which may exacerbate the development of abnormal behaviours.
Horses are trickle feeders – they eat a small amount of food throughout the day. Oral stereotypies are often exhibited after the provision of a meal and may therefore be a response to low-gut fill and reduced opportunity to perform feeding behaviours. However, there is increasing evidence that these behaviours may also be linked with problems associated with the feed causing digestive problems.
Less frequent provision of roughage in the diet and higher levels of concentrated grain-based foods may increase stomach acidity to levels where the horse experiences discomfort. As such it has been hypothesised that abnormal crib-biting and wind-sucking behaviours could develop as a coping-mechanism to reduce the level of discomfort to the horse. In fact recently it has been demonstrated that crib-biting foals showed a greater degree of ulceration and inflammation in their stomachs than foals which did not display the behaviour. It is therefore important to investigate the possibility that your horse has underlying gastric problems and to treat them where possible using your vet.
The provision of an antacid diet has recently been shown to not only improve the stomach condition of stereotyping horses but to reduce the behaviour. The behavioural response to supplementary antacid provision was most effective for post-feeding crib-biters, and, interestingly, was just as effective in horses that had been doing the behaviour for a long time.
Currently the treatment is not a cure-all and we do not know the long-term effects of feeding mineral based supplements such as these on the horse’s health; but we are moving closer to understanding the causes and treatment of these frustrating behaviours.

There is good evidence that risk of developing oral stereotypies is lower if the horse has as natural a lifestyle as possible. This would therefore involve:

  • Grass feeding (or at least a high fibre diet).
  • As much turn out as possible.
  • As much social contact as possible.
  • Avoidance of concentrated feed, especially carbohydrate (grains and sugars)-based ones (fat and fibre-based are less acidic).
  • Natural, gradual weaning.

Management changes appear to be most effective at reducing the behaviour, although this may depend upon the individual horse and the history of the problem. In general:

  • Increase turn out and social companionship.
  • Provide ad-lib, high fibre, variable forage in the stable.
  • Treat any gastric problems such as ulcers.
  • Supplement with antacid in the diet.
  • Avoid feeding concentrates, especially carbohydrate-based ones.

Attempting to prevent the horse from crib-biting is not generally recommended, such as the use of:

  • Surgical procedures where the nerves or muscles enabling the animal to carry out the behaviour are severed/altered.
  • Punishers such as electrical collars and cribbing collars with sharp points.
  • Anti-crib surfaces such as metal boards or nasty-tasting pastes.
  • Use of medication.

Since these prevent the horse from performing the behaviour without treating the cause. Horses with these problems have been shown to be highly motivated to perform these behaviours and will perform them at higher levels after they have been prevented. If they are crib-biting to relieve discomfort or improve their digestion (whether they are aware of this or not) then preventing them from doing so may be harmful.
One study has shown that preventing crib-biters from performing the behaviour led to slower gut movement which may have an impact on any digestive problems. Since the behaviour is often not directly harmful to the horse, enabling them to perform the behaviour on a less harmful surface (where teeth are protected), such as a robust rubber coating over the stable door (a cribbing bar/post) may offer the horse a more appropriate outlet.