Plasma cortisol and faecal cortisol metabolites concentrations in stereotypic and non-stereotypic horses: do stereotypic horses cope better with poor environmental conditions?

Results showed that 1) plasma cortisol and faecal cortisol metabolites concentrations did not differ between horses displaying stereotypic behaviours and non-stereotypic horses and 2) both oral and motor stereotypic behaviour levels did not predict plasma cortisol or faecal cortisol metabolites concentrations.Cortisol measures, collected in two large samples of horses using both plasma sampling as well as faecal sampling (the latter method minimizing bias due to a non-invasive sampling procedure), therefore do not indicate that stereotypic horses cope better, at least in terms of adrenocortical activity.Stereotypic behaviours are repetitive behaviours induced by frustration, repeated attempts to cope and/or brain dysfunction [1,2]. Stereotypic behaviours typically appear in sub-optimal life conditions, i.e. known or believed to be aversive, e.g. physical confinement, social isolation and/or food deprivation. Why and how such behaviours arise nevertheless remains a highly debated issue. One explanation, commonly known as the “coping hypothesis”, is that stereotypic behaviours may help the animal to “cope” with unfavourable conditions, by providing an “enrichment” in the sub-optimal domestic situations [2] or by counteracting physical discomfort [3]. In striped mice Rhabdomys, stereotypic animals even have a better reproductive output [4], suggesting that some stereotypic behaviours may have beneficial effects. In horses, stereotypic mares however exhibit lower reproductive success [5], and at present, the coping function of stereotypic behaviours remains a highly debated issue. According to the coping hypothesis, individuals that display stereotypic behaviours are expected to have lower physiological stress levels (commonly assessed by measuring glucocorticoids concentrations) than non-stereotypic animals in the same sub-optimal environment. Attempts to link stereotypic behaviours with glucocorticoids however have yielded contradictory results. For example in horses,