Olfactory-based interspecific recognition of human emotions: Horses (Equus ferus caballus) can recognize fear and happiness body odour from humans (Homo sapiens)

Emotional recognition has been demonstrated to occur between members of different species. However, the majority of studies on interspecific communication of emotions so far focused on the senses of vision and hearing while the contribution of the sense of smell has rarely been studied in this context. Thus, the aim of our study was to assess if horses display differential behaviour in response to human fear and non-fear odour. Body odour samples were collected from 10 adult humans (Homo sapiens) in fear and happiness condition, respectively. The human body odour samples collected in these two conditions, together with a control condition, were then presented to a total of 21 horses (Equus ferus caballus). We found that the horses displayed some differential behaviour in response to human fear and non-fear odour. The horses lifted their heads significantly more frequently and for longer in the fear and in the control condition compared to the happiness condition. Similarly, the horses tended to touch a familiar person that was present during the test more frequently and for longer in the fear condition compared to the happiness condition. Additionally, depending on odour condition, the horses differed in the time they spent keeping their ears back. These results can be explained in the context of the process of domestication which may have favoured the development of the ability to recognize heterospecific emotions. To conclude, in the present study we provide evidence for a possible purely olfactory recognition of human emotions by horses.