Expert Q & A

Horses can smell human fear
What that means for equine clinicians

By Adam Marcus

Horses can bring a sense of calm to agitated humans, but we don’t always return the favor. Not only do equids respond to our voices and body language, but they also appear to smell our fear and anxiety, too, according to French researchers. In a recent study, the scientists found that horses exposed to cotton pads containing the sweat of people who had been exposed to frightening films exhibited skittishness and other fearful behaviors (see page 19).

Plotine Jardat, DVM, PhD, who trained as a veterinarian and now is a researcher in ethology at the French Institute for Horse and Riding in Nouzilly, France, was the lead author of the study, which appears in the journal PLOS One. The Modern Equine Vet spoke with Dr. Jardat about the findings and their implications for clinicians who care for horses.

MEV: Were you surprised to find these effects? Was there any reason to assume horses would not be responsive to this kind of sensory stimulation?

Dr. Jardat: We were surprised to see that human body odors can really impact horses’ behavior and physiology. It is a common belief that horses and other mammals can ‘sense’ our emotions, but before this research, we were not sure what cues they used or to what extent they could be affected. It was not obvious that chemical signals from humans could be perceived and interpreted by another species such as horses.

MEV: Equine veterinarians often operate in high-pressure situations in which they, their technicians, or even animal owners might be anxious. What does your study say about the importance of keeping a calm bedside manner—not just in terms of body language, but in managing physiological stress?

Dr. Jardat: Indeed, our findings indicate that keeping a calm bedside manner can help avoid transmitting a stressed emotional state to the horse. It’s not only about body language, which practitioners and owners can modulate voluntarily, but also about the actual emotions one is experiencing, which can modulate the body odors we produce and, in turn, the horse’s behavior and physiology.

MEV: This research suggests a form of emotional contagion between species may be possible. In clinical scenarios where a horse is acting out, and where clinics typically have focused on physical restraint or sedation, do you see a role for olfactory masking or the use of calming scents to neutralize the human fear odors that might be inadvertently fueling the horse’s agitation during a procedure?

Dr. Jardat: I think this might be a way of managing emotional contagion through odors. But what recent research actually suggests is that horses perceive and react to our emotions using diverse cues, including facial expressions and the tones of our voices. So, I’m not sure that masking odors would be sufficient for that purpose. This would need to be tested in a separate experiment.

MEV: Could this olfactory sensitivity be a primary reason for the ‘Dr. Jekyll and Mr. Hyde’ behaviors some horses exhibit between their owner and a calm professional trainer? How might the findings apply to, say, the evaluation of a horse before purchase?

Dr. Jardat: Yes, these findings can help understand why a horse would behave differently in the same training situation depending on the emotional state of the human leading them. For example, if the owner is afraid while leading a horse toward an obstacle, the horse might perceive the fear and be more afraid itself than when being led by a more calm, joyful trainer.

MEV: Previous studies (see, for example, this article in the Equine Veterinary Education journal, established that veterinary clothing can serve as a microbial fomite. Your work suggests clothing may also carry emotional information. Does this reinforce the need for practitioners to change scrubs or outer layers between highly stressful emergencies and routine wellness exams, not just for pathogen control, but to avoid importing the chemical scent of a previous crisis into the next stall?

Dr. Jardat: Our findings do suggest that clothing might carry chemical emotional information that could cause horses to react. Moreover, research in the human domain has shown that it is mainly in the armpit sweat where odors vary with emotional state. So, in cases where a practitioner has been through a highly emotional state and the clothes that the next horse is going to be able to smell are in contact with the practitioner’s armpits, it might indeed be interesting to change these clothes before the next horse. MeV