Possible influence of neighbours on stereotypic behaviour in horses

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Abstract

Revealing risk factors of abnormal stereotypic behaviour (ASB) in horses can help in the design of protective measures. Previous epidemiological studies indicate that social isolation, housing, management conditions, and feeding regime have a strong effect on developing ASB. The common belief that exposure to a stereotypic horse increases the risk of ASB has never been substantiated. Here we report that a generalised linear mixed models (GLMM) analysis of data on 287 horses of nine riding schools revealed that exposure to a stereotypic neighbour is a significant risk factor for performing stereotypy. Also, aggressive behaviour towards other horses increased the odds of stereotypy in the aggressor. These correspondences are unlikely to be a riding-school effect, because riding schools were treated as random factor in the GLMM. Risk factors identified by epidemiological studies cannot be treated as causal agents without independent evidence. Our aim in presenting these findings was to draw attention to the possibility of neighbour effects so that other researchers would include this variable in their surveys.

Introduction

In the broad sense, stereotypies are repetitive, relatively invariant actions. Stereotypies are considered abnormal when they occur without any primary function and might be detrimental to the health or performance of the animal (Mason, 1991). The prevalence of the most common abnormal stereotypic behaviour (ASB) in horses, such as crib-biting/wind-sucking, weaving, and box-walking have been reported at a level of 0.4–5% (McBride and Long, 2001, Mills et al., 2002, Bachmann et al., 2003, Christie et al., 2006), however, with wood-chewing included, overall ASB reached 20–35% of prevalence (McGreevy et al., 1995a, Waters et al., 2002). Such stereotypies have been implicated as a possible cause for gastric ulceration and colic (Nicol et al., 2002, Archer et al., 2004) and for tooth wear, weight loss, and weak condition (McBride and Long, 2001). Once established, ASB are difficult to change; therefore prevention is of great concern.

Long lasting stereotypies together with a variety of other abnormal behaviour can be precipitated by chronic stress as a consequence of restricted milieu at early age in many species (Mason, 1991). This process is reversible by environment enrichment but only at early life which, together with neurobiological evidence suggests a critical period for the neuroprotective effects of complex social and physical milieu (Hadley et al., 2006). On the other hand, temporary stereotypies as normal displacement behaviour are often elicited by acute stress caused by inhibition of the appetitive phase of a goal directed behaviour (Hughes and Duncan, 1988). For example, non-stereotypic horses often performed weaving, nodding, and oral stereotypies when their companions were fed concentrate (Cooper et al., 2005). Although, such displacement behaviours are not abnormal, they are considered prerequisite for ASB (Waters et al., 2002). Sequences of behaviour starting with displacement followed by ASB can be observed even in ASB horses (Ninomiya et al., 2007). Unfortunately, as most caretakers do not note such mild symptoms, we, as others in previous studies, had to narrow our survey to true ASB.

Previous studies indicate that breed type, feeding regime, housing, and management conditions have a strong effect on developing ASB (McGreevy et al., 1995b, Waters et al., 2002, Bachmann et al., 2003, Christie et al., 2006). According to anecdotal evidence, exposure to other horses engaged in stereotypies is a risk factor for developing similar habits (Houpt and McDonnel, 1993). However, controlled experiments or epidemiological studies have never supported such beliefs (Cooper and Albentosa, 2005).

The effect of neighbours on horses with established stereotypies is controversial. On the one hand, it has been suggested that a poster image of a conspecific (Mills and Riezebos, 2005), a mirror in the paddock (McAfee et al., 2002, Mills and Davenport, 2002), or visual contact with other horses (Cooper et al., 2000, Mills and Davenport, 2002) effectively reduced the time spent in weaving. However, any treatment in those studies was limited to 2–5 days, a short period of time for habituation. Possible facilitation of weaving by exposure of weavers to non-stereotypic horses (Cooper et al., 2000) was also limited by the experimental design, because the two individuals with highest level of ASB were exposed to each other rather than to non-weavers. On the other hand, observation of horses visually isolated or being able to see each other as a consequence of housing revealed that weaving was higher among horses whose boxes faced that of other horses than among horses whose boxes did not (Ninomiya et al., 2007).

The aim of this study was to investigate risk factors of ASB in horses. We show that exposure to a stereotypic neighbour may have significant effect on the odds of horses performing abnormal stereotypies.

Section snippets

Data collection

We performed a questionnaire survey to detect potential risk factors of ASB (crib-biting/wind-sucking, wood-chewing, weaving, and box-walking) on 287 horses by visiting nine riding schools in Hungary.

Before asking the horse-owners to complete the questionnaire, we explained them the definition of stereotypic and other behaviour problems (according to McGreevy et al., 1995b) During our 4–6 h stay at each riding school we observed stereotypic behaviour in all horses reported to have ASB. The

Housing conditions and prevalence of behavioural disorders

In the population of 287 horses sampled, the prevalence percentage of crib-biting/wind-sucking was 4.53% (N = 13), wood-chewing was 10.10% (N = 29), weaving was 2.79% (N = 8), and box-walking was 3.83% (N = 11). The occurrence of any of the four listed abnormal behaviours (ASB in general) was 16.70% (N = 48). Aggression towards horses was noted in 17.07% (N = 49) of individuals, aggression towards people was 9.41% (N = 27), behaviour problems during riding was 9.06% (N = 26), and door or tier opening behaviour

Discussion

Prevalence of abnormal stereotypic behaviour (ASB) in Hungarian riding schools was not different from those of other countries (McBride and Long, 2001, Christie et al., 2006). However, factors associated with ASB revealed by our analysis are in apparent contrast with previous epidemiological surveys. Management methods restricting natural behaviour have been suggested as major risk factors for developing ASB. Oral stereotypies (crib-biting/wind-sucking and wood-chewing) are mostly associated

Acknowledgements

We are grateful to Dr. A. Harnos for her help in statistical analyses. Dr. G. Bodó, Dr. J. Kis and Dr. V. Bókony gave valuable advices in the course of our studies. Dr. T. O’Keeffe and Dr. J. Kis commented the manuscript. We thank K. Gavalda and Z. Varga for assistance in the field.

References (28)

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