Stereotypies are repetitive, invariant compulsive behavioural sequences often observed in captive or domestic animals. Owing to the relative infrequency of their observation in wild- or free-ranging animals, stereotypies are assumed to be a product of captivity (1). Stereotypies are more commonly observed in animals kept in social isolation or sub-optimal environments lacking sufficient species-relevant enrichment (2); thus, their presence is often considered to be an indicator of poor welfare (3). Domestic horses, particularly those kept in intensive housing systems (boxes, stalls, etc.) show a range of stereotypic behaviours, including oral (crib-biting) and locomotor (weaving) behaviours (4).
One strong risk factor for the development of stereotypic behaviour is social isolation (5, 6) and isolation rearing is known to be a strong risk factor for the development of stereotypic behaviours in horses (7). Despite this, relatively little is known about the mechanisms that link social behaviour and stereotypies. It may be that social deficits are a risk factor and/or important in the pathogenesis of stereotypic behaviour. In support of this hypothesis, studies have shown that social isolation results in increased cortico-striatal oxidative stress markers in rodents (8) and that crib-biting horses have increased levels of several oxidative stress markers at rest, which further increase during crib-biting behaviour (9). Moreover, crib-biting is linked to increased dopamine activity within the striatal nuclei in the midbrain (10), suggesting that crib-biters may be in a permanent hyperdopaminergic state, with dopamine metabolism being responsible for a number of oxidative free-radicals (11).
Collectively, this evidence suggests a possible link between social behaviour, social interactions and stereotypic behaviour. In particular, sub-optimal social events may increase the oxidative free-radical status of the animal, via shifts in dopamine physiology, to produce the stereotypy phenotype. Furthermore, there is substantial evidence to suggest that free radical levels can be significantly reduced through the ingestion of antioxidants (12). Antioxidant supplementation may therefore have the exciting potential to reduce stereotypy development in animals predisposed to this abnormal behavioural condition.
Aims and objectives:
The central aim of this PhD is to understand the role of social and neurobiological factors in the development of stereotypic behaviour. First, the student will examine social behaviour in stereotypic, and non-stereotypic horses utilising both direct observation of natural behaviour and experimental manipulation (e.g., watching controlled, dyadic interactions). The hypothesis for this first phase is that stereotypic horses will differ in the quality and quantity of social interactions. Secondly, neurophysiological functioning will be assessed. Specifically, dopaminergic function will be assessed via validated behavioural and psychological tests (cognitive tasks and SBR) to confirm the link between stereotypic behaviours and oxidative stress. Physiological assays will also determine oxytocin and cortisol levels. Finally, the student will explore whether socio-behavioural deficits are a cause or consequence of stereotypic behaviour. The effects of changes in the social environment (social isolation versus group housing) on behaviour will be monitored and the dietary intake of subjects will be experimentally manipulated (via the introduction of food supplements) to determine whether these interventions decrease stereotypic behaviour and reverse socio-behavioural deficits.
How to apply:
We welcome applications from highly motivated prospective students who are committed to develop outstanding research outcomes. You can apply online at http://www.port.ac.uk/applyonline
. Please quote project code PSYC4100218 in your application form.