Horses recognise disgust in humans.

Disgusted? Don’t show your horse.

In keeping with the findings by Léa Lansade’s team in France, a Japanese study has found that horses recognise when humans show facial and vocal expressions of disgust—and they change their behaviour because of it.

“Horses are sensitive to humans’ negative emotional cues, so we do not think that people should show negative emotions to horses carelessly in their daily life because horses may receive stress from human negative emotions,” said Ayaka Takimoto-Inose, PhD, of the Department of Behavioural Science in the Graduate School of Humanities and Human Sciences, and the Centre for Experimental Research in Social Sciences, both at Hokkaido University in Sapporo, Japan.

Takimoto-Inose and her colleagues tested 14 horses to observe their behaviours when a human expressed either happiness, neutrality, or disgust in reaction to a looking behind a black screen. The experimenters had set up black opaque barriers to give the horses the impression that something was hidden behind the barriers. Then one researcher would look behind the barrier and act happy (smiling and saying, “Wow!”), neutral (no reaction), or disgusted (crinkling the face and saying, “Eww!”).

They found that generally speaking, the horses followed the human’s gaze less frequently and for a shorter period of time when the human expressed disgust, Takimoto-Inose said. “Maybe they were avoiding the hidden object because the human found it disgusting, or maybe they were avoiding the human because she was making expressions of disgust; we don’t know,” she explained.

To the researchers’ surprise, however, the horses actually didn’t show any significant differences in behaviour between the happy and neutral expressions. This might have been because the horses lived in groups at pasture and spent little time with humans. “It’s possible they didn’t have enough exposure to humans to connect their facial and vocal expressions with positive emotions,” she said. Negative emotions might be more critical for them to recognize since they could indicate a threat, she added. “Dogs have also been shown to have difficulty distinguishing between neutral and positive facial expressions in humans, so it might not be as easy for animals as the negative emotions are,” Takimoto-Inose explained.

This test with the neutral expression was an important feature of their study compared to several other studies on horses’ reactions to human emotions, according to the researchers. “In other studies, the scientists didn’t compare horses’ responses in the two conditions (positive and negative) with those in the neutral condition,” Takimoto-Inose said. “We tested horses’ responses in all three conditions. This allowed us to show that horses can evaluate the human disgust emotion as a negative emotion absolutely (as opposed to just being “not happy”).”

The effects of human emotions on horses and other domestic animals represent an essential field of scientific study, she explained. “Domestic animals, especially dogs and horses, have built a close and cooperative relationship with humans, which suggests that social signals, such as emotional information, play important roles in how these animals live and interact with humans,” said Takimoto-Inose. “Therefore, how these animals perceive emotional signals and what roles the signals play are important questions to investigate.”

The study is published in Animals: Are Horses (Equus caballus) Sensitive to Human Emotional Cues? by Chihiro Baba, Masahito Kawai and Ayaka Takimoto-Inose. It is open access and can be read in full here.