Researchers led by Plotine Jardat, working with colleagues from the Institut Français du Cheval et de l’Équitation and several French research institutions, conducted a study to explore whether horses can detect and respond to emotional information carried in human body odours. The work focused on olfactory communication, a sensory channel that is widespread in animals but still poorly understood in the context of human–animal interactions.
(c) Jardat et al. PLoS one. CC-BY 4.0
Olfaction plays a central role in communication for many species, particularly in social and emotional contexts. While previous research has mainly examined olfactory signals within the same species, emerging evidence suggests that chemosignals may also operate between species. This study investigated whether human emotional states, specifically fear and joy, can be perceived by horses through smell, and whether these odours influence equine behaviour and physiology.
The experiment involved 43 adult Welsh mares housed at the Animal Physiology Experimental Unit of l’Orfrasière (UEPAO) in Nouzilly, France. Human odours were collected from volunteers using cotton pads placed in the armpits. Volunteers wore the pads while watching 20 minutes of either fear-inducing (horror) or joy-inducing film clips. To minimise confounding factors, participants followed strict hygiene routines and dietary restrictions for two days prior to odour collection. Unused cotton pads served as a control condition.
During testing, each horse was fitted with a disposable lycra muzzle positioned over the nostrils. Attached to the muzzle were either two unused cotton pads (control group) or two pads from a single volunteer collected in either a fear or joy context. Horses were exposed to only one odour condition.
The experimental protocol consisted of both human–horse interaction tests and fear-related tests. In the morning, horses completed a grooming test and a free human approach test, designed to assess their willingness to interact with a person. In the afternoon, they underwent a suddenness test, involving an unexpected stimulus, and a novel object test, which assessed reactions to an unfamiliar item. Alongside behavioural observations, physiological measures were collected, including heart rate and salivary cortisol levels, to evaluate stress and emotional arousal.
The results showed clear differences between odour conditions. Horses exposed to fear-related human odours interacted less with the experimenter during the human approach test and displayed stronger fear-related behaviours than horses exposed to joy-related or control odours. Specifically, horses in the fear condition touched the human significantly less and spent more time gazing at the novel object, indicating heightened vigilance. They were also more strongly startled by sudden stimuli.
Physiological data supported the behavioural findings. Horses in the fear group showed significantly higher maximum heart rates compared with those in the joy and control groups, suggesting increased emotional arousal. Post-hoc analyses confirmed these differences, and principal component analysis revealed an overall pattern of heightened fear responses and reduced human interaction when horses were exposed to fear-related odours.
The authors concluded that human emotional body odours can influence both behaviour and physiology in horses. Sweat samples collected during fearful situations induced greater fear responses and reduced willingness to engage with humans, whereas joy-related odours did not produce these effects. These findings highlight the importance of chemosignals in interspecific emotional communication and raise interesting questions about how domestication may have shaped horses’ sensitivity to human emotional cues.
From a practical perspective, the study suggests that a handler’s emotional state may influence horses not only through body language and voice, but also through smell. For horse owners, trainers, and equine professionals, this research underlines the potential value of remaining calm and emotionally regulated during interactions, as emotional signals may be transmitted in ways that are subtle yet biologically meaningful to horses.
For more details, see:
Jardat P, Destrez A, Damon F, Tanguy-Guillo N, Lainé A-L, Parias C, Reigner F, Ferreira VHB, Calandreau L, Lansade L.
Human emotional odours influence horses’ behaviour and physiology.
PLoS One (2026) 21(1): e0337948.
No comments:
Post a Comment