Whorl judging of horse temperament and personality may have found its scientific grounding.

Ever notice that donkeys have very different temperaments compared to horses?

Ever notice that donkeys have very different heads compared to horses?

If you’re starting to think now that those differences could be linked, you might be right. According to Canadian and Australian researchers, the physical aspects of the skulls and the brains they house may have some connection with the personalities of these two kinds of equids.

Forehead width, the position of the olfactory lobes (small lobes in the front of the brain that process smell), and the location of hair whorls differ considerably between horses and donkeys, perhaps providing some neurophysiological basis for behavioral differences, said Katrina Merkies, PhD, associate professor and equine behavior researcher at the University of Guelph, in Canada.

“The idea of external landmarks with underlying anatomy and how that relates to behaviour is fascinating,” said Merkies, working in collaboration with Paul McGreevy, BVSc, PhD, MRCVS, MACVS (Animal Welfare), professor of animal behavior and animal welfare science at the University of Sydney. “So we were looking for a relationship between skull morphology and temperament, which has been previously documented in dogs. Our results supported these findings.”

Merkies and McGreevy, together with Georgios Paraschou, veterinary pathologist at the Donkey Sanctuary in the UK, examined the heads of 14 Standardbred horses and 16 donkeys of several breeds after they had been euthanized for other reasons. They took measurements of lengths, widths, and angles of various skull and brain features as bases for comparison.

They found that donkeys had a much greater cranial index than horses, she said. The cranial index is defined as the width across the forehead (between the “temples”) compared to the length of the face from the poll to the mouth. Essentially, this means that, proportionally speaking, donkeys have wider foreheads. While that may seem obvious to most people by looking at donkeys and horses, the scientific confirmation of that difference in width is important, Merkies explained.

What isn’t obvious to the naked eye, though, is the difference in position of the olfactory bulbs in the brain. While horses have fairly large olfactory bulbs located directly in front of the brain, the olfactory bulbs of donkeys are smaller and rotate more inward, she said. This could possibly affect the sense of smell, but it could also affect emotions, as the activity of the olfactory lobes is known to be associated with other parts of the brain related to social and emotional responses.

A rather unexpected, yet ‘serendipitous’ finding was the position of the hair whorls on these animals, said Merkies. Although their location on horse heads varied sometimes significantly from horse to horse, they always ended up being within about 1.5 cm of the location of that horse’s olfactory lobes hidden underneath the hair, skin, and bone. In donkeys, however, the whorl was always located much farther down the face from the olfactory lobes, seemingly unrelated to the position of the lobes themselves.

“I certainly didn’t start with that hypothesis, and in fact I wasn’t even looking at the whorl at first,” said Merkies. “It was only when I was taking the measurements of the olfactory bulb in the horse heads, and placing markers on the skull to identify the location of various structures in the photos I took, that I noticed that often, my marker was placed on the whorl. That was rather cool! Later, when I analyzed the donkey skulls, the whorl was noticeably distanced from the olfactory bulb.”

The finding might actually yield scientific credibility to commonly held beliefs about whorls, she added.

“There is already a lot of folklore surrounding whorl locations and patterns,” Merkies said. “It could be purely coincidental, but I don’t believe much in coincidence. The olfactory lobe does play a crucial role in social interactions, memory, and learning. It may be that those folklore tales do have some credibility if there is some causal relationship between whorl placement and influence of olfactory lobes on behaviour….”

That popular folklore suggests that a whorl above the eyes indicates a difficult horse, one between the eyes indicates a manageable, “uncomplicated” horse, and one below the eyes indicates an intelligent and less reactive horse. Given that the whorls and the olfactory bulbs develop from the same embryonic tissue at about the same time, the age-old concept of whorl-judging might have some scientific grounding, according to Merkies. And that would make sense in light of her new discovery about donkeys’ whorls, that they’re consistently positioned much farther underneath the eyes than what she’d seen in horses.

“The finding that whorls are located more down the nose in donkeys than in horses may be related to their less reactive temperaments,” she said.

Does that mean horses aren’t as “smart” as donkeys, then?

Not at all, according to Merkies. “The definition of ‘smart’ is based on our human interpretation,” she said. “I say that donkeys are really smart at being donkeys, and horses are really smart at being horses.”

More importantly, a better understanding of the temperaments of each equid could lead to more appropriate training for that individual, more realistic expectations, and, ultimately, better welfare, she said.

The study is open access: Morphometric Characteristics of the Skull in Horses and Donkeys—A Pilot Study by Katrina Merkies, Georgios Paraschou and Paul McGreevy