The health impact of behaviours such as crib-biting and weaving

  • Horses who crib-bite, weave and so on are often frowned upon in the equestrian world. But do some behaviours have greater effects on health than others? Professor Debra Archer FRCVS investigates

    Many owners want to know how to stop cribbing and other undesirable equine behaviours such as wind-sucking, box-walking, weaving and other traits typically described as stable vices. But as these stereotypic behaviours develop to help some individuals cope with a life where they cannot forage, move around or interact with other horses as nature has designed them to do, is preventing a horse from expressing the behaviours that help it cope the best action to take?

    Why it shouldn’t be described as a vice

    A “vice” is a behaviour, habit or other negative trait that a person has. But animals don’t have that level of thinking; they aren’t doing these behaviours deliberately.

    One study estimated that around 2.7 million horses worldwide display some form of stereotypic behaviour. These horses don’t need punishment, just a better understanding of why they are doing this and, ideally, methods for preventing these behaviours from developing in the first place.

    Stereotypic behaviours include crib-biting, wind-sucking, weaving and box-walking. These are common, developing in around one-fifth to one-third of all horses. Their cause is complex and considered to be a combination of genetics and management.

    Stereotypies are not seen in wild horses and are generally considered to be a coping strategy that some domestic horses develop. The behaviour helps these horses to adapt to a life in which they cannot feed, roam and interact with other horses, as they have evolved to do in the wild.

    Stereotypies can be a cause of major concern and frustration to some horse owners and carers. In addition, they can reduce the financial value of these horses and can make them more difficult to sell or rehome. But how do they affect a horse’s health, and what can we do to help?

    Crib-biting and wind-sucking have been studied most in terms of effects on horse health. These so-called “oral stereotypies” involve complex linking between the brain and gut, something we do not yet fully understand. Therefore, it is not surprising that most health effects in these horses relate to the mouth and gastrointestinal tract.

    Some horses may crib-bite or wind-suck only occasionally, usually around feeding time or at other specific times, such as when tied up. Other horses perform this behaviour almost constantly and it is likely that the severity of crib-biting and wind-sucking behaviour is more significant to health than simply the fact that a horse displays these behaviours.

    Crib-biting can affect both the teeth and skull. It can cause increased wear on the incisor teeth, although there is no current evidence that this causes specific dental issues. Horses that crib-bite or wind-suck, especially youngsters, can fracture the front (incisor) part of their jaw if they are startled and suddenly pull back while their teeth are grasping a fixed object. Fortunately, these types of fractures are usually relatively simple to repair and have a good prognosis.

    Interestingly, there is some evidence from the USA and Japan that crib-biting or wind-sucking may be associated with arthritis of one of the joints within the horse’s skull. This condition, temporohyoid osteoarthropathy (THO), is relatively uncommon in horses. But when researchers looked at the clinical records of horses with THO, those affected were eight to 12 times more likely to be a crib-biter or wind-sucker.

    Affected horses display head tilting or head shaking, ataxia (where they cannot coordinate their legs or balance properly), paralysis of the eyelid on the affected side and drooping of the muzzle. Diagnosis is based on endoscopy of the guttural pouch, X-rays or ideally computed tomography, and a horse may require medical treatment or surgery.

    In horses in whom unusual signs related to the head such as head-tilt or head shaking develop, it is worth investigating THO as a potential cause of such signs, particularly in a horse that crib-bites or wind-sucks.

    A chance of colic

    Several studies have shown that crib-biting and wind-sucking are associated with an increased chance of colic. Importantly, a study performed at the University of Liverpool’s equine hospital showed that the frequency and duration of crib-biting behaviour was hugely important; the more often and longer the horses performed this behaviour, the more likely they were to have suffered from colic before.

    Crib-biting and wind-sucking don’t increase the risk of all forms of colic, but these horses are more likely to develop large colon impactions and epiploic foramen entrapment, in which the small intestine becomes stuck through a natural opening within the abdomen. Surgical techniques have been developed to close the epiploic foramen in horses that develop this type of colic, as it can recur.

    Gas colic, gastric ulcers and weight loss have also been associated with these behaviours. These might also be related to the severity of the behaviour; a horse that is crib-biting or wind-sucking for long periods of time during the day is likely to swallow a reasonable amount of air or spend less time eating.

    The link between gastric ulceration and crib-biting or wind-sucking is not fully understood but both are associated with diet, particularly the need for forage to be available for large parts of the day such as through increased pasture access and small-holed haynets to encourage trickle feeding.

    Despite the fact that abnormal hoof wear and issues relating to strain on joints and tendons and muscle fatigue are stated as problems in horses that box-walk or weave, there is actually very little scientific evidence to back this up.

    It would seem possible that repetitive abnormal movements that occur with these “locomotor” stereotypies could result in musculo-skeletal issues developing, but further research is needed in this area.

    Should we stop undesirable behaviours like cribbing?

    This is a controversial topic and in general, the answer is no. This should be a last resort where management changes fail to make a difference and where the horse’s health is genuinely being negatively affected.

    Studies have shown that physically preventing horses from performing stereotypic behaviours causes increased stress and they find other ways to cope – for example, weaving inside the stable itself if bars have been fitted to the stable door. Some described methods are barbaric and are simply not acceptable in terms of horse welfare.

    The focus should be on trying to find ways to help these horses cope better – for instance, increased access to forage and turnout, interaction with other horses, fitting of stable mirrors so the horse can see his reflection, a change in type of stabling or in location on the yard so the horse isn’t in isolation on its own. These changes may not stop horses from cribbing or demonstrating other behaviours, such as wind-sucking, but it would seem logical that reducing the duration of time for which horses display these signs would benefit their health and welfare.

    What does the future hold?

    In humans, a huge amount of research is being done to explore how genetics affect development of different diseases and how genes affect our behaviour. This work is expensive to perform, but rapid improvements in technology and reduced costs of performing genetic studies are allowing us to understand more about the role of genetics in disease and behaviour in animals.

    This ultimately may lead to better understanding of the genes that are associated with stereotypic behaviours in horses. This could allow horses, particularly youngstock, that are more likely to develop these behaviours to be identified, managed and monitored more carefully. In addition, it could allow drugs to be developed to help reduce the severity of stereotypic behaviours if these behaviours have already become established.

    For the moment, the main focus must be on preventing these behaviours from developing in the first place, rather than wondering how to stop cribbing and other undesirable behaviours once they are established. Optimal management of youngstock, particularly around weaning and introduction to training, is critical.

    Once established, these behaviours are frustrating to manage and can have various negative effects on health. Yards where large numbers of horses develop or display stereotypic behaviours must consider different ways of management to ensure sufficient access to forage, pasture exercise and social contact with other horses.

    Ref Horse & Hound; 12 November 2020


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