Chestnut Hanoverian horses have a reputation for being sensitive. Kylie Heitman didn't know that when she purchased her mare Lena, who is trained for a form of competition riding known as dressage.
"She is quite sensitive and high-strung," Heitman says, adding that it was a challenge to keep the horse calm when she tried introducing her to new objects or skills. "She's quite opinionated, too."
Heitman, a biology student at Albion College, wondered if lavender oil, known for its calming properties in humans, could help relax horses during stressful events, such as when they're transported in trailers to performance events. To find out, she conducted a research study, and presented the results in a poster session at the 2017 Experimental Biology conference. Some of her findings fall in line with a handful of previous experiments that show that lavender oil reduces stress in animals, including dogs, sheep, mice, cats and also humans.
"There is a biological pathway for lavender to affect the part of the brain that is the primary modulator of stress in an animal," says Edward Ferguson, assistant professor of animal sciences at McNeese State University in Lake Charles, Louisiana. In 2012, Ferguson published a small study showing that lavender oil decreased the heart and respiratory rates of seven horses, following a period of high stress.
From previous experiments on mice conducted by other scientists, Ferguson came to understand how. When an animal becomes stressed, for example a mouse smells a cat nearby, a part of the brain called the amygdala sends a signal to the body to release adrenaline and cortisol. Adrenaline helps gives the body a boost of energy to respond quickly, like run away. Cortisol modulates stress over a longer period, releasing glucose slowly so that the body can respond to additional threats, even if the mouse eludes its predator.
Lavender appears to modulate receptors found in the amygdala, reducing the stress response, Ferguson says.
Heitman was familiar with Ferguson's work as she had discovered it when scanning the scientific literature of related studies. Although she did find some experiments that dealt with other animals, including dogs, mice, and sheep, she found no other research but Ferguson's that dealt with horses.
She used the experiment as a starting point, but wanted to measure cortisol levels. Working with eight horses from Albion College's Nancy G. Held Equestrian Center, Heitman ran two experiments separated by three weeks. In each case, horses were loaded into a two-horse trailer, driven 5.5 miles (8.9 kilometers) for 15 minutes and then unloaded.
Before loading the horses, Heitman measured each animal's heart rate and drew blood to test later for cortisol levels. A second heart rate measurement and blood draw happened immediately after the horses were unloaded from the trailer after the trailer ride.
During the ride, Heitman held a diffuser near the horses' noses. Four of the horses received a lavender oil treatment during the ride and four received scentless water vapor. At the end of the ride, the horses were taken out of the trailer and after a 50-minute recovery period, blood was drawn and the heart rates measured.
When Heitman repeated the experiment three weeks later, she flip-flopped the therapy, so that horses that had received the lavender oil the first time received water vapor the second time and vice versa.
Horses that received the lavender oil aromatherapy had significantly lower cortisol levels than those who had received the scentless water vapor. She also found a small decrease in heart rate, but it was too small to be significant.
When lavender is used in a diffuser, says Ferguson, two chemical components are released: linalool and linalyl-acetate — the two components that affect the receptors in the amygdala.
He pointed to a study from 1991, from scientists at the University Vienna and the University of Innsbruck, who tested lavender oil on mice that had been injected with caffeine. The aromatherapy reduced the effects of caffeine by 67 percent.
"Lavender prevented the caffeine from stimulating the nervous system," says Ferguson.
In a different study, Deborah Wells and her team at Queens University in Belfast looked at the effects lavender, chamomile, rosemary and peppermint had on 55 rescued dogs living in a shelter. The researchers exposed the dogs for four hours a day, five days a week to the essential oils, including a period with no aromatherapy.
They found that when the dogs were exposed to lavender and chamomile, they spent more time resting and less time moving than when exposed to rosemary, and peppermint or when there was no scent at all. The dogs also spent less time barking.
"Diffusing odorants with sedatary properties into the dogs' quarters may result in a slightly less stressful environment for the animals housed within," the authors write.
"Lavender has a biological effect on animals," says Ferguson.
To what extent will require additional research. Ferguson says he would want to study which receptors were affected by the lavender and how they influenced the fight-or-flight response.
Heitman has applied for another grant to further analyze blood samples from her experiments. If she had the time and resources, she would conduct experiments using different essential oils, increase the time exposed to the essential oil or put the horses under other stressful situations.
Is she going to use aromatherapy on her horse Lena?
"That would probably be good," she says.