An unexpected acoustic indicator of positive emotions in horses

Amongst different acoustic productions, horses produce sneezing snorts that are assumed to be a way of freeing the airways and facilitating breathing. Observations revealed that they are produced more in some equestrian facilities than others and, within facilities, in some individuals more than others, without clear relationships with air conditions. In the present study, we hypothesized that these sounds may reflect more than just a hygienic function and may, as a consequence of a physiological change related to mild positive excitations, reflect the psychological state of the animal. In order to test this hypothesis, were observed 47 horses which belonged to three different populations: 2 in riding schools with restricted life conditions, the third was composed of leisure horses living in naturalistic conditions. Behavioural observations of their spontaneous behaviours were performed in stalls and pastures. The frequency of sneezing snorts, their context of production as well as behavioural indicators of welfare (e.g. abnormal repetitive behaviours) were recorded. The results show that 1) the naturalistic-like population emitted significantly more sneezing snorts than riding school ones in comparable contexts, 2) the riding school horses produced twice more sneezing snorts in pasture condition than in stall, 3) this acoustic production was significantly associated with positive situations (e.g. while feeding) and was associated with ears in forward or sidewards positions (reflecting more positive internal states), 4) the frequency of sneezing snorts was negatively correlated with some welfare measures and especially the composite total chronic stress score (reflecting compromised welfare) :the lower was the TCSS, the higher was the sneezing snort rate. These four results converge to indicate that sneezing snorts could reflect a positive physiological and emotional state. This study leads us to believe that this acoustic signals could constitute a potential marker of positive emotions in animals.