by Gerrard Flannigan & Joseph Stookey
The horse is an extremely gregarious animal which lives in a variety of small, sometimes complex, social groups. There are primarily two separate social groups found in wild horse populations: the harem led by a dominant stallion with 5 to 8 mares and their foals and the bachelor herd made up of sexually mature surplus males who band together until they are able to establish and maintain a harem. The daily activity pattern of wild horses includes frequent social interactions with their herdmates plus movement within their home range. Over 50% of their day is spent grazing.
The daily activity pattern of our tame or domestic horse is considerably different than its wild counterpart. Our current practices, including the social groupings, feeding schedules and housing, have dramatically altered the frequency and diversity of behaviours we observe in stable horses compared to feral horses. Many horses, in both pleasure and performance industries, spend the majority of their time in individual stalls. They have limited opportunity to interact with another horse and little chance to graze. In the absence of these naturally occurring behaviours, many horses will perform "stable vices".
Stable vices, also known as stereotypies, are derived from normal sequences of motor activity such as oral, locomotor, grooming or sexual behaviour; they differ from normal behaviour because they are repetitive and serve no obvious function. Common equine stall vices include weaving, cribbing, wind sucking, head bobbing, pawing and self mutilation. Horses are not unique in the animal kingdom at performing repetitive and "purposeless" behaviours. Stereotypies have been reported in most zoo animals, all of our domestic livestock, and companion animals. Without exception, stereotypies are seen when animals are placed in restrictive environments, deprived of social contact or on restricted diets. As a result, stereotypies are generally considered indicators of poor welfare.
Studies from Ontario and the United Kingdom estimate that between 15 and 30% of horses show these behaviours. The expression of any behaviour is dependent on a combination of genetics and environmental influences. There are individual differences in how a horse will react to a given husbandry system. Consequently, horses under identical conditions will show different types of stereotypies or not express them at all. Likewise, some individual horses will not develop stereotypies even though a close relative may have, especially if they are kept under different conditions.
How do stereotypies develop? One theory is that animals are motivated to perform a naturally occurring behaviour and if that behaviour is prevented or thwarted, it results in a chronic state of arousal. Once a critical level is reached, the animal performs an abnormal behaviour, such as a stable vice, in an attempt to decrease that arousal. Another theory is that most sequences of behaviour include two distinct phases: an appetitive phase, where the animal is motivated to perform a behaviour and a consummatory phase where the animal completes the behaviour to reduce the initial drive (ie. courtship is an appetitive behaviour terminated by mating). If the animal is unable to reach the second phase, it returns to the original sequence and begins again. Eventually the initial behavioural act becomes a fixed pattern which is refined until it barely resembles a normal behaviour.
In the horse industry, the animals performing stereotypies are often labelled "bad actors", no doubt a carry-over from the term "stable vice" which implies a negative act. It is also widely believed, but remains scientifically unproven, that stable vices can spread as a result of having a "bad actor" in the stable. Even if the behaviour can be learned from watching other horses, it is a mistake to focus the attention onto the individual horse rather than the environment or factors contributing to the expression of the stereotypy. For the animals perform them, stereotypies may be coping mechanisms to dissipate their anxiety. Simply preventing the display of the behaviour with aversive therapy (ie. electric shock, restrictions), drugs or surgery without eliminating the initial stressor does not alter the anxiety of the animal and would be cruel. In a recent British questionnaire-study by McGreevy and co-workers, management factors had the greatest influence on the risk of stereotypic expression. They found an increased risk when less than 6.8 kg/day of forage was offered. They found and increased risk when good quality hay was offered. The authors postulated that the increased level of protein may be too different from the forage they would normally select while grazing. An alternate explanation is that the high quality hay may meet their nutritional requirements faster than it satisfies their drive to engage in the physical act of eating. They also found an increased risk when horses were kept in stall designs that did not allow contact between horses. Other workers have found that daily exercise was beneficial in reducing wood chewing among stabled horses.
These are valuable findings that should be utilized to prevent stereotypies, especially since we know that once established, stereotypies are very difficult to treat or reverse. The behavioural requirements of the horse must be considered in the design of husbandry systems. Systems which fail to meet the need for social contact, exercise and lengthy foraging periods are likely to have horses which develop stereotypies. Group housing in large paddocks is probably the best method of keeping horses. However, if horses must be confined, the ideal stall would allow visual and physical interaction between neighbouring horses. The ideal management system for stabled horses would also include an adequate exercise regime and enough forage to satisfy their need to graze.
As horse owners, we have the responsibility of keeping both physically and psychologically sound animals. Unfortunately, current husbandry systems are not meeting the basic behavioural needs of our horses. We can meet these needs by incorporating recent research into our facility and management practices. Ultimately we believe, at the W.C.V.M., that we can maximize the welfare of horses by using the knowledge we already have and continue to research, identify and study the factors that contribute to the incidence of stereotypies.
Article orginally appeared in the Spring 1996 issue of Horse Health Lines a publication of the University of Saskatchewan, Western College of Veterinary Medicine, Equine Health Research Fund.
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