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Horses can smell fear, or at least whether you have scared yourself witless watching a horror movie, according to researchers who say the effect has consequences for riders, trainers and others who work with the animals.
In a series of tests, horses that smelled body odour from people watching scary films startled more easily, had higher heart rates and approached their handlers less often than when the odour came from people watching more joyful scenes.
If the finding holds up in future studies, it would suggest that fear is contagious between humans and horses, with volatile compounds in human sweat acting as a warning signal that danger may lurk nearby.
“This study shows how closely connected animals and humans are,” said Dr Léa Lansade at the University of Tours in France. “Unconsciously, we can transmit our emotions to animals, with quite important effects on their own emotions in return.”
Smell is one of the most common and primitive senses used to communicate, but research often focuses on scent signals that pass between members of the same species – to find mates, for example – rather than those that cross species barriers.
Lansade and her colleagues investigated whether horses responded to the smell of fear in human sweat, the product of a cocktail of compounds that other people can sense even if they are never aware of it.
Before the experiments, volunteers watched film and sketch scenes while wearing cotton pads in their armpits. The participants saw clips from the horror movie Sinister, or more joyful scenes from films such as Singin’ in the Rain.
To see how horses responded to fearful and joyful odours, the scientists stapled the cotton swabs to the animals’ muzzles, positioning them directly over the horses’ nostrils.
Tests then assessed how frequently the horses approached and touched their handler, and how they reacted when an umbrella suddenly popped open in front of them as they munched on a bucket of food.
Writing in the journal Plos One, the scientists describe how horses were more startled, had higher peak heart rates, and made less contact with their handlers when exposed to sweat from the scared people. Measurements of the stress hormone, cortisol, found no differences, however.
Dr Plotine Jardat, the first author on the study and a researcher at the French Horse and Riding Institute near Tours, said while people might struggle to control the odours they emitted, riders and those caring for horses should be aware of their emotions and the impact they could have.
“Arriving relaxed and in a positive mood can foster a better interaction with the horse, whereas if you are afraid yourself, the horse can feel afraid in response and react more strongly to a potentially scary situation,” she said.
Prof Biagio D’Aniello at the University of Naples Federico II has shown that both horses and dogs can smell human fear.
“The findings add to growing evidence that emotional signals can cross species boundaries, with horses reacting to human fear via smell,” he said. “This raises intriguing questions about how human stress or calmness might shape everyday human-horse interactions, from training to clinical handling.”
