Vice - or self-help?

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Stress is defined as 'mental, emotional or physical strain or tension'.
In response to chronic (long-term) stress, the body secretes a family of steroid hormones called corticosteroids. These have undesirable effects on the tissues that are responsible for producing white blood cells, which make up part of the body’s defence system. The number of white blood cells produced is reduced, resulting in an increased susceptibility to infection and disease. This is why people who are stressed are more likely to suffer illnesses such as irritable bowel syndrome, as well as more minor ailments such as colds. Similarly, horses which are subject to excessive stress are likely to develop stomach ulcers and/or be generally unthrifty.

Antidotes to stress

Endorphins are the brains own opiates - they are similar in structure to chemicals such as morphine and heroin. Endorphins are released in response to stress, and appear to have similar calming effects to those of opioid drugs
Certain activities appear to boost or prolong release of endorphins from the brain i.e. they can give an opiate 'hit'. Some repeated, relatively invariant sequences of movements which outwardly appear to have no purpose seem to be both stimulated by the release of endorphins and also prolong that release. These types of movements are known as 'stereotypies'. They are a means by which animals can give themselves the equivalent of a Valium.

Examples of stereotypies in horses are actions such as weaving, box-walking, cribbing and windsucking. Most people are more familiar with the term 'vices' to describe these types of behaviour, however this word is misleading in that it implies that horses are making moral decisions to act in an evil manner. In reality, nothing could be further from the truth - the behaviours are simply the horses response to whatever stressful situation it has been placed in.
Horses are by no means the only animals which exhibit stereotypies in stressful situations - other examples of stereotypies include rocking movements and repetitive vocalisations in institutionalised humans, bar chewing in stalled sows, head swinging in zoo-housed bears and elephants, pacing in captive fennec foxes, eye rolling in veal calves and jumping in caged bank voles.

Why do some horses develop stereotypies while others do not?
There is a strong belief among people who own or care for horses that normal horses will copy the stereotypies of afflicted stable-mates. It is much more likely that a horse who appears to imitate a stereotypy was experiencing the same stressors as the animal it appears to have copied, and so reacted in a similar way. Horses in a yard are likely to be under similar management routines and therefore subject to the same stressors. Equally, a horse which already has a well-developed stereotypy will pose no threat if it is introduced to a yard with a horse-friendly management system.

There is also no evidence to show that stereotypies are inherited. ALL behaviours are the result of the effects of the genes of an individual combined with the effects of their environment, which act in different proportions in different situations. Thus there is probably a small amount of genetic predisposition for horses to perform stereotypies - this would explain why certain horses develop stereotypies though other horses kept in the same environment and managed identically do not. This can be seen in humans too - some individuals are better able to cope with stress than others.

What are the stressors which lead to the development of stereotypies?
Horses have spent the past six million years evolving to suit a particular lifestyle. They are built to spend around 16 hours every day moving around slowly while chewing on fibrous vegitation, and to live in family groups in large, open spaces.
Any factors which remove the horse from its natural environment will cause it stress. These include spending large amounts of time in the stable, not having access to ad lib forage and being deprived of companionship.
Conversely, allowing horses to perform as much of their evolved behavioural repertoire as possible will reduce the risk of the development of stereotypies and may also reduce the amount they are performed in horses which already have established stereotypies.

Development of stereotypies.
Stereotypies tend to develop from the main frustration that the animal faces, for instance a horse which is deprived of the behaviour it would perform in the wild to find food is likely to develop some sort of oral stereotypy such as windsucking.
Feeding-related stereotypies are further explained by evidence which shows that grain-based (‘high sugar’) feeds actually stimulate endorphin release, resulting in enhancement of stereotypic behaviour patterns. Decreasing the amount of grain fed to stereotypic horses, therefore, may reduce the rate of stereotypy performance. A diet based on high quality hay rations may reduce stereotypy directly by minimising endorphin release, as well as indirectly through leading to more time being spent chewing and eating.
Recent evidence suggests a further cause of windsucking and cribbing stereotypies. These types of stereotypy are peculiar to horses - many other animals show weaving or pacing behaviour but no others are known to perform anything resembling cribbing or windsucking. This could be connected with the horses unusual digestive system, which is designed to cope with large amounts of fibrous material and huge volumes of digestive secretions. Horses which are fed mainly on small volumes of concentrate feed may have problems digesting the high levels of sugar which are present in these feeds, which can lead to the digestive tract becoming acidic. In these horses it is thought that cribbing and windsucking may be a means by which they can increase the levels of secretion of digestive fluids and so help dilute the acidity of the lower digestive tract.

Once fully developed, stereotypies will usually be performed in any stressful situation, i.e. they become independent of their original eliciting stimulus. Fully developed stereotypies may not show the current state of the horse, but reflect a past challenge severe enough to have traumatic effects on the central nervous system. This is why horses which have developed a stereotypy will often carry on performing it even when their environment has been improved.

So if stereotypies are actually beneficial to animals, why do we want to treat them?
The moral argument that stereotypies are simply a symptom of stress, and subjecting animals to stress is ethically wrong comes top of the list. Successful treatment of stereotypy involves the removal of the stressor which caused the behaviour in the first place. A secondary factor is that some stereotypies can be damaging to the animal in themselves, for instance cribbing results in damage to the incisor teeth; weaving can result in concussion injuries to the front limbs.
As already discussed, treatment involves returning the animal to as natural an environment as possible i.e. with access to ad lib forage, space and companionship. In cases of weaving and box-walking this alone should be enough to eliminate stereotypy.
In cases of cribbing and windsucking, however, the stereotypy tends to be more persistent, the animal is in effect addicted to its Valium. It is possible that these animals are suffering from chronic low-grade pain from which the stereotypic behaviour may provide relief. This area is currently receiving research interest.

In conclusion, it is evident that stereotypies are much more complex than their common name, vices, would suggest. Stereotypic behaviour gives us an indication that all is not well with particular individuals, and lead us to consider horses which are subject to many stressors but which do not develop stereotypies - are they coping better with the situation or are they simply not coping at all?

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