Horses with clockwise (top), anticlockwise (bottom)hair whorls. Credit: J Murphy & S Arkins

Whether the hair on a horse's head curls around clockwise or anticlockwise can tell you whether it is right- or left-hoofed, say researchers in the Republic of Ireland. Clues to which direction a horse favours could help trainers produce animals that run straighter and — perhaps — win more races.

Veterinarians Jack Murphy and Sean Arkins of the University of Limerick classified a total of 219 racehorses, show-jumpers and eventers as left- or right- hoofed based on the judgement of expert riders as well as on tests such as which hoof they led with when beginning to walk, and which side they chose to go round an obstacle.

Of 104 left-hoofed horses, the researchers found that 78 or 75% had anticlockwise hair whorls. And out of 95 that favoured their right side, 64 or 67% had clockwise whorls. The study is published in Behavioural Processes1.

That is a strong enough link to be a useful tip to trainers, says Murphy. A horse's handedness or 'motor laterality' translates into a tendency to drift in one direction — which can make a big difference to a horse's competitive chances. The earlier you can spot biases, he says, the easier it is to correct them, by, for example, getting horses to work on their weaker side using 'lungeing', when the animal circles its trainer at the end of a long lead.

A racing chance

A racehorse's laterality is an often-overlooked factor in deciding its chances, says Murphy. Trainers have told him that for a strongly biased horse, the direction of the bends on a racecourse can have the same effect as a handicap of 10 kilos or more.

The Epsom Derby's famous left-hand curve, Tattenham Corner, may have proved the undoing of many a fancied right-sider, he adds. And the sharp turns on show-jumping courses can be even more influential.

"I've spoken to many of the top riders," says Murphy, "and they'll tell you 'I'm not going to be competitive', or 'I've got a good chance', depending on the turns on the course, and what direction their horse prefers."

But you shouldn't bet your shirt based on a glimpse of a hair whorl, he adds. Besides the imperfect link between hair and hoof, factors such as a race's distance and going are probably much more significant to its outcome. "Laterality is a small part of the mix, but there are so many variables," says Murphy.


Both hair patterning and handedness reflect asymmetries produced in brain development, and may be controlled by the same genes. There is also evidence that the hair of right-handed humans is more likely to lie in a clockwise pattern, and vice versa for left-handers.

"Humans also have turning biases," says neuroscientist Mike Nicholls of the University of Melbourne in Australia. "Some people claim that most people turn leftwards, though this is disputed. It's interesting to note, however, that when people jog around a park, they usually go anticlockwise."

Laterality has been seen in vertebrates from fish, to birds, to mammals. But species vary in how strongly they prefer one side, and whether a majority is right- or left-sided. It's been suggested that an asymmetrical brain may help to reduce redundancy and conflict between brain regions. Another idea is that in flocking and schooling animals, turning biases might help coordinate mass movements.

"Of all the animals, humans are the most lateralized in terms of the complexity and variety of behaviours that are asymmetrical," says Nicholls. This might have something to do with the evolution of language and intelligence, he adds. "By looking at asymmetries in other species, and the context in which it occurs, it allows us to understand what is so special about the human brain."

Credit: Punchstock