Fat diet reduces stress and intensity of startle reaction in horses

Intense startle reaction by horses is a common cause of injuries for both riders and horses. Some studies suggest that diet composition, in particular the percentage of fat, may have an effect in stress and behavioural response to novel stimuli. Here we use 28 individual horses to perform an experiment on the influence of diet treatment on physiological parameters and behaviour. We compared a control starch–sugar diet with a diet with higher proportion of fat but the same total energetic content. Physiological and behavioural responses were measured for diet types, both at rest and when exposed to a startling visual stimulus. Our results demonstrate that the increment of fat proportion in the diet reduces the level of stress at resting and the intensity of response to startling stimuli, as denoted both in physiological parameters and in behavioural variables. We conclude that increasing the fat content in diet may be a valuable tool to reduce horse stress and the risk of accidents.