From The Magazine: Getting A Feel For Equine Sensory Hairs

Dec 3, 2021 - 8:00 AM

Horses have adapted in many ways over millennia to be able to escape from predators and survive in the wild: They have long faces that house intricate structures for a strong sense of smell, skin so sensitive it will twitch when a fly touches it, and a set of some of the largest eyes in mammals.

But there’s one sensory organ that’s often overlooked: vibrissae, better known as whiskers. These long hairs on the muzzle and around the eyes are useful sense elements for horses, but many riders trim them for a tidier appearance. While horses can survive without their vibrissae, the trimming of them is starting to be seen as a horse welfare issue as people learn more about their function and extrapolate research done with other species to horses.

As of July 1, the Fédération Equestre Internationale has banned the trimming of sensory hairs around the muzzle and eyes, which follows longstanding bans due to horse welfare concerns in some European countries.

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Trimming sensory hairs around the muzzle and eyes is now banned in international competition due to horse welfare concerns. Lindsay Berreth Photo

Andrew McLean, Ph.D., BSc, Dip Ed, is an equine behavioral science expert at Melbourne University Equine Hospital in Australia, the CEO of Equitation Science International, a former top-level eventer and has experience working with race horses and in elephant welfare. He’s studied the significance of equine vibrissae, but he says their function hasn’t been examined as extensively as it has with other mammals, such as rats or manatees. Research on equine sensory abilities has focused much more on hearing and vision.

But unlike a human’s beard, equine whiskers are embedded much deeper in their skin, and they help horses feel their surroundings.

“Each one of them is lodged in its own blood capsule with lots of nerves,” said McLean. “The idea of the blood capsule is that even the smallest movement of the whisker itself is perceived by sensory receptors and goes straight to the brain. They’re considered to be high sensitivity—in other words, low-threshold receptors— because it only takes the tiniest movement to trigger the information release.”

Not Your Average Hair

While whiskers are made of keratin like the hair on a horse’s body, they’re much different. Their follicles are five to six times larger than a regular hair follicle. In mammals like rats that are born naked, whiskers are the only hairs on the body at birth.

“They’re the first hair to develop on an embryo,” McLean said. “They don’t molt like normal body hair does. Hair on primates is never that sensory—it’s just hair—whereas it is very much in many animals like horses and dogs and cats. It’s a pretty unique, specialized structure. In some animals it even helps maintain balance; in aquatic mammals that swim it maintains their balance and orientation when swimming. Manatees have really strongly developed vibrissae.”

When a horse is grazing, scientists believe whiskers help them feel the ground—not unlike a human using their fingertips and hands to explore their environment— while being able to keep their eyes on the lookout for danger. The muzzle area is a blind spot, so whiskers can help a horse be aware of an incoming object. Horses use their noses to investigate objects, food and fellow herd members, and whiskers likely help them explore their surroundings. (Hairs around the eyes also help the horse feel around his environment and prevent eye injuries.)

There are two types of whiskers—macro-vibrissae, which are thicker and longer and help determine distance and width of an object, and micro-vibrissae, which are shorter and thinner and found closer to the mouth. Researchers believe the latter are more important for object recognition than spatial tasks.

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There are two types of whiskers—macro-vibrissae, which are thicker and longer and help determine distance and width of an object, and micro-vibrissae, which are shorter and thinner and found closer to the mouth. Amy Dragoo Photo

In rats, each whisker connects to its own separate location in the brain, which indicates their importance, but it’s not known if that’s the case with horses. Studies have found that rats are severely disabled if their whiskers are trimmed. Though scientists know whiskers are sense items in horses, more specific research is lacking.

“We do know they’re more prone to head and eye injury [when whiskers are trimmed], but we don’t know much else,” said McLean.

He added that there are no published studies that explain how they affect a horse mentally.

“I was involved in writing the latest model of the five domains, which also included human/animal interactions, and we really don’t know much about those sorts of depravations in terms of the mental affect—an animal’s mental security and what it does to it—because we haven’t been able to do that,” he said. “It’s possible to
do experiments, for sure. They’re called judgement bias tests. I think that’d be a very good thing to do, but you’d have to get ethics approval to shave off a horse’s whiskers just to do it. It might actually show once and for all, but it’s a really detrimental thing.”

In 2013, Machteld van Dierendonck led a study at Utrecht University in the Netherlands to look at the function of vibrissae and the effects of trimming them.

The group applied stimuli to the whiskers of 14 horses— heat, cold, damage, electricity and traction—for five seconds. Behavior and heart rate were analyzed. No significant heart rate changes were noted, but the researchers commented that heart rate might not be the right outcome to measure.

They also tested horses in three groups, with shaved, trimmed and untrimmed whiskers, looking at behavior and nose-bump rates in a small bucket.

“No conclusions can be drawn from these results regarding the effect of trimming vibrissae on the used parameters,” reported the published study results. “Analyzed parameters do not appear to be useful outcome measures.”

An Issue Of Animal Welfare

Germany became the first country to ban whisker removal in 1998, followed by Switzerland in 2014. In 2019, France banned the practice. The FEI rule passed unanimously when it was voted on at the FEI General Assembly in December 2020. (No ban on the trimming of ear hairs was enacted because they. are not considered sensory.)

“This is ultimately about horse welfare and ensuring horses are not deprived of an important sensory mechanism, and it provides the FEI community with a harmonized and international approach by aligning with legislation already in place at a national level in several of the FEI’s member nations.” said Dr. Jenny Hall, chair of the FEI Veterinary Committee and an FEI board member.

The full rule, Article 1004, states: “Horses are not permitted to compete in FEI Events: i) if the Horse’s sensory hairs have been clipped and/or shaven or in any other way removed unless individual sensory hairs have been removed by a veterinarian to prevent pain or discomfort for the Horse. Areas of hair that must be clipped, shaven or removed to allow veterinary treatment are exempt from this rule.”

A spokesperson for the FEI added, “This rule was instigated based on the committee members’ wide understanding of current animal welfare and behavioral science and clinical experience rather than in response to any specific scientific study that has been recently published.

“It is important to note that the members of the FEI Veterinary Committee are elected for their expertise and knowledge of equine health and welfare in the broadest terms. So they have both the insights and the experience of applying science to safeguard the welfare of equine athletes,” continued the FEI statement.

The U.S. Equestrian Federation has not passed a rule banning the trimming of sensory hairs for national competitions.

“[USEF] does not currently have plans to implement a similar rule for national-level equestrian competition but encourages members to consult with their own veterinarians when making decisions about their horses’ care and grooming,” said an emailed statement from a federation spokesperson.

Although he feels the new FEI whiskers rule should have passed long before it did, McLean is pleased to see progress on animal welfare in horse sports. He noted that anything the sports can do to make themselves better for the horses involved also gives them better standing when it comes to public perception.

“This idea of social license is sort of the latest word in animal welfare,” he said. “Social license to operate is basically about the fact that it doesn’t matter what experts think, or it doesn’t matter what experienced horse people think—it really matters how the general public perceive what you do and the community expectations of how we treat animals, and the reassessment of practices is really what is driving all of this through likes on Facebook. If organizations like the FEI don’t remain ahead of the game, it’s going to set the whole thing back. The next thing that happens if you’re not ahead of the game, legislation comes in.”

He pointed to a ban on greyhound racing in New South Wales, Australia, after it came to light that the industry was using live bait during races. The sport was banned within a month, but in the years since has been allowed to come back more regulated.

“That’s a good example [of what happens] if you’re not ahead of the game,” he said. “I think we have to be aware of these possibilities in the horse world. That’s not hard—to still have really good interactions with horses and maintain horse sports as long as they’re more regulated, and we take care of the horse’s welfare.”


This article ran in The Chronicle of the Horse in our Nov. 22 & 29, 2021, issue.

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