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Dogs have long been celebrated for their ability to sense human emotion, making them man’s best friend, but new research has found they are not the only ones.
A new study has uncovered that horses possess the same skill, specifically smelling human fears.
Researchers from the University of Tours in France found that when horses were exposed to scent samples from humans experiencing fear, they became more reactive.
The horses had elevated heart rates and were more hesitant to approach handlers compared with reactions triggered by scents linked to positive emotions.
Similar to dogs, horses in the study detected chemical signals released in human sweat during emotional states. These chemosignals are made up of volatile compounds that change when a person is stressed or anxious.
While dogs developed the ability through domestication, the researchers suggested horses’ ability is tied to survival, as the animals are hard-wired to notice signs of danger in their environment.
Dr Léa Lansade at the University of Tours in France said in a statement: ‘This study shows how closely connected animals and humans are.
‘Unconsciously, we can transmit our emotions to animals, with quite important effects on their own emotions in return.’
When humans feel fear, the body releases stress hormones such as adrenaline and cortisol, which change the chemical makeup of sweat.
These changes cause the skin to emit a different mix of odor molecules known as volatile organic compounds.
Fear-related sweat often contains higher levels of compounds such as aldehydes, ketones, fatty acids, and steroid-related chemicals like androstadiene.
Although these chemicals have little or no smell to humans, animals with highly sensitive noses can detect them. Together, these chemical shifts create a scent signature that signals stress or danger.
The new study looked at whether horses can pick up these compounds in human sweat.
Researchers placed cotton pads in the armpits of humans while they watched frightening or happy videos, and then put the pads near the nostrils of 43 female horses.
Some horses were also exposed to clean, unused pads for comparison.
Cotton pads carrying human odors were placed near the horses’ nostrils while the animals underwent suddenness tests with unexpected events, novelty tests involving unfamiliar objects, and human interaction tests such as approaching or being groomed by a handler, as scientists measured their behavior and heart rate.
The results showed that horses exposed to scents from frightened humans reacted more strongly.
They were more easily startled, had higher heart rates, stared longer at unfamiliar objects and were less likely to approach or touch a person.
Horses exposed to ‘happy’ scents or neutral odors showed calmer behavior.
The findings suggested that horses can sense human emotions through smell and that fear can be passed from people to horses without any words or gestures.
‘The fact that different species appear to respond to each other’s emotional chemosignals is interesting, as emotions have previously been viewed as mainly internal states that serve to regulate individual behaviors and produce signals that inform conspecifics of danger or resources,’ the team shared in the study.
‘The fact that these signals transcend species boundaries suggests that they could also play a role in interspecific interactions, especially between humans and domestic mammals.’
A 2020 study found that horses feel pain similar to humans.
A team from the University of Sydney found both have ‘no significant difference’ in nerve endings in the outer pain-detecting layer of skin.
Although horses do have a thick layer of tissue on the skin’s surface, researchers say it is not strong enough to protect the animals from ‘external cutaneous pain.’
Thoroughbred racing began in America after British settlers brought the animals across the Atlantic in 1665, but it did not become an organized sport until after the Civil War in 1868.
And a key part of this event is jockeys whipping their horse with the hopes of beating the rest to the finish line.
However, the team found that these creatures have evolved to feel pain when whipped as much as humans.
This conclusion is based on 10 years of research that, according to the team, ‘could rock the racing industry.’
The team used microscopic skin samples from 10 dead humans and 20 euthanized horses to explore the differences or similarities in the anatomic structures.
The results show that there is no significant difference ‘in either the concentration of nerve endings in the outer pain-detecting layer of skin (epidermis) or in the thickness of this layer,’ according to the study published in the journal Animals.
The samples showed that the dermis of the horse’s skin is thinner than that of humans, but this area does not involve pain detection.
And although horse skin is thicker, it does not protect them from the pain of being hit with a whip.
‘This finding challenges assumptions about the physical capacity of horses to feel pain, particularly in comparison to humans, and presents physical evidence to inform the discussion and debate regarding the ethics of whipping horses,’ the team wrote in the study.
