Sniffing lavender could help soothe horses, a study has suggested.

Researchers at the University of Arizona discovered horses’ heart rate variability reduced while they were inhaling the scent of lavender oil.

Isabelle Chea, an undergraduate student at the time, and Ann Baldwin, professor of physiology and psychology at the university, conducted the study. The findings were published in the Journal of Equine Veterinary Science.

“We wanted to test regular horses that [weren’t] stressed out by external forces,” said Baldwin, who is herself a rider.

“Some horses and some breeds, it’s just in their nature that they are more stressed. So, we wanted to use horses that were not being scared deliberately to see what effect, if any, the aromatherapy had on them.”

Nine dressage horses of varying breeds and ages, all based at the same yard, were used in the trial.

Each horse was led to a paddock and held while a diffuser containing lavender oil was held near his nose.

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A monitor tracked heart rates and heart rate variability for 21 minutes — seven minutes before the introduction of the diffuser, seven minutes with the diffuser in close proximity, and seven minutes after it was removed.

“The heart rate didn’t change; what changed is what’s called the parasympathetic component of heart rate variability,” said Ms Baldwin.

“One of the parameters of heart rate variability is RMSSD [root mean square of the successive differences], and that represents parasympathetic input, which is the relaxation part of the autonomic nervous system.

“If RMSSD goes up, that indicates the horse is relaxed. We found that when the horses were sniffing the lavender, RMSSD significantly increased compared to baseline.”

Horses also showed signs of relaxation, including lowering their necks and licking and chewing while inhaling the scent.

The experiment was repeated with water vapour and chamomile, neither of which produced a similar calming effect or increase in RMSSD.

“We did get a calming effect with the lavender, but when we measured afterward, we no longer had the effect,” Baldwin said. “So, it’s just during the sniffing of the lavender that we see this calming effect.”