Cookies on VetMed Resource

Like most websites we use cookies. This is to ensure that we give you the best experience possible.

 

Continuing to use www.cabi.org  means you agree to our use of cookies. If you would like to, you can learn more about the cookies we use.

VetMed Resource

Veterinary information to support practice, based on evidence and continuing education

Sign up to receive our Veterinary & Animal Sciences e-newsletter, book alerts and offers direct to your inbox.

News Article

Eyelid twitches and blink rate as a measure of stress in horses


Observation of eye blinks and eyelid twitches could provide useful information on the stress level of horses, researchers suggest

A horse will blink less and twitch its eyelids more when it’s under mild stress, researchers at the University of Guelph have found.

The study, published in the journal Animals, is thought to be the first to reveal the significance of eyelid twitches as an indicator of stress, says Prof. Katrina Merkies, the study’s lead author.

“With humans, we already know our blinking changes when we are under pressure. Some studies have shown we blink more when agitated while others found we blink less. We wanted to see if horses blink rates change too,” said Merkies, a professor in the Department of Animal Biosciences at the Ontario Agricultural College.

“When we train horses, we specifically teach them to suppress their stress responses because we don’t want horses to react when they are startled or nervous. But even if they’ve learned to suppress their reaction, it doesn’t actually decrease the stress they feel,” she said.

While stress can be measured through heart rate monitors or blood cortisol levels, Merkies and her team wanted a non-invasive measurement, so they decided to test whether a horse’s eyes could offer clues.

They recruited 33 horses of various breeds from three riding lesson facilities in eastern Ontario and exposed them to three mildly stressful scenarios.

In the first, a ball was thrown in front of the horse in an attempt to startle the animal. In the next, the horse was visually separated from its herd for a few minutes. Finally, the horse’s food was withheld for three minutes at feed time while its herd mates were allowed to begin eating.

The researchers filmed the horses, watching for changes in eye and ear movement, head tilt and general restlessness.

They found that withholding the feed for a few minutes was the most stressful for the horse as indicated by its increased heart rate, restlessness and head movement. Conversely, separation and the startle test evoked little response.

“It’s important to remember these were riding school horses, so they were used to being startled and being separated. But the withholding of food was new, so that’s likely why they became stressed,” she said.

When researchers reviewed videos of the horses’ eyes during feed withholding, they noticed the horses blinked less but twitched their upper eyelids more.

On average, the horses’ full blink rate decreased to an average of five blinks per minute during the stress compared to the eight to nine times per minute when relaxed. During the feed restriction, when the horses felt the most stress, their eyelid twitches increased from an average of two twitches per minute to six twitches per minute. There was no increase in eyelid twitches with the other stress tests.

Article: Merkies, K., Ready, C., Farkas, L., Hodder, A. (2019). Eye Blink Rates and Eyelid Twitches as a Non-Invasive Measure of Stress in the Domestic Horse. Animals 9(8), 562; doi: 10.3390/ani9080562

Article details

  • Date
  • 12 November 2019
  • Source
  • University of Guelph
  • Subject(s)
  • Horses and other Equines