Abstract
The aim of our study was to explore the association between dominance rank and body condition in outdoor group-living domestic horses, Equus caballus.Social interactions were recorded using a video camera during a feeding test, applied to 203 horses in 42 herds. Dominance rank was assigned to 194 individuals. The outcome variable body condition score (BCS) was recorded using a 9-point scale. The variables age and height were recorded and considered as potential confounders or effect modifiers. Results were analysed using multivariable linear and logistic regression techniques, controlling for herd group as a random effect.More dominant (p=0.001) individuals generally had a higher body condition score (p=0.001) and this association was entirely independent of age and height. In addition, a greater proportion of dominant individuals fell into the obese category (BCS≥7/9, p=0.005).There were more displacement encounters and a greater level of interactivity in herds that had less variation in age and height, lending strength to the hypothesis that phenotypic variation may aid cohesion in group-living species. In addition there was a strong quadratic relationship between age and dominance rank (p<0.001), where middle-aged individuals were most likely to be dominant. These results are the first to link behavioural predictors to body condition and obesity status in horses and should prompt the future consideration of behavioural and social factors when evaluating clinical disease risk in group-living animals.
Highlights
Dominance refers to an ordering between group-living animals, not necessarily linear (Appleby, 1983), which dictates the priority of access to resources. Drews (1993) defines this neatly as: “an attribute of the pattern of repeated, agnostic interactions, between two individuals, characterised by a consistent outcome and default response rather than escalation of conflict”
Our study presents strong evidence that dominance status may be associated with body condition in domestic outdoor-living horses, and this association appears to be entirely independent of both age and height, both of which have been shown to be important determinants of dominance in horses in previous studies (Rutberg and Greenberg, 1990; Sigurjónsdóttir et al, 2003)
The feed trial method used here allowed for a competitive, food-related assessment of dominance and related behaviours
Summary
Dominance refers to an ordering between group-living animals, not necessarily linear (Appleby, 1983), which dictates the priority of access to resources. Drews (1993) defines this neatly as: “an attribute of the pattern of repeated, agnostic interactions, between two individuals, characterised by a consistent outcome and default response rather than escalation of conflict”. Dominance refers to an ordering between group-living animals, not necessarily linear (Appleby, 1983), which dictates the priority of access to resources. Drews (1993) defines this neatly as: “an attribute of the pattern of repeated, agnostic interactions, between two individuals, characterised by a consistent outcome and default response rather than escalation of conflict”. Dominance behaviours have evolved as a means of peaceful and quick conflict resolution in group-living animals (Bernstein, 1981; Drews, 1993; Hemelrijk, 2000). Group living is an important strategy for some grazing herbivorous species such as horses, who rely on vigilance and flight as a means of avoiding predation (Hamilton, 1971; Krause and Ruxton, 2002). S.L. Giles et al / Applied Animal Behaviour Science 166 (2015) 71–79
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