Tuesday, May 31, 2011

Polydactyl Horses (and People): Why Are Some Horses Born with an Extra Hoof?

This polydactyl was found in British Columbia by one of the farrier students at Kwantlen College. Gerard Laverty, the instructor at Kwantlen, sent these images to me, which started my collection. Image © Hoofcare Publishing and Gerard Laverty.
If you visit farms and horse barns in New England, you'll sooner or later find one with a clan of double-pawed cats. Their owners are usually quite proud of them and love to show off their big mitts. The condition is so common around here that most people don't give it a second thought. A lot of people actually prefer them, especially if they are Maine Coon Cats.

But when the equivalent of a "double paw" shows up on a giant Shire draft horse, people notice.
So it must have been for "Norfolk Spider" back in the early 1900s in England. The giant Shire carried extra toes on both front feet, which must have occasionally been quite painful when and if they hit each other.

When an animal is born with an "extra" digit, the disorder is known as a polydactyl, polydactyly, or polydactylism. The words are used, or misused, as if interchangeable. "Poly", of course, means "many", and "dactyl" comes from the Greek word "daktylos", for "digit".

The extra hoof (or paw, etc.) is called a "supernumerary digit".

Probably the best and most often quoted opinions on polydactyl horses were in papers published  in Scientific American in the 1880s and 1890s by Professor O.C. Marsh of Yale University's natural history department. They are still interesting to read today, and you can find scanned versions of them on the web.

This blog post was inspired by an old post card of what must have been a famous horse in England at one time: Norfolk Spider. Look closely! He was known as the six-footed Shire. Vintage post card is protected by copyright and is reproduced here courtesy of collector Christine Sutcliffe. (Thank you!).

According to Professor Bruce McFadden, PhD, Curator of Vertebrate Paleontology at the Florida Museum of Natural History, and author of Fossil Horses: Systematics, Paleobiology and Evolution of the Family Equidae, the prized horses of Alexander the Great (Bucephalus) and Julius Caesar had extra toes. 

But what about the polydactyls of today? Professor McFadden has only witnessed the phenomenon firsthand once, in a yearling Quarter Horse. This horse is the subject of a paper written by three French authors, and published in The Journal of Veterinary Science; the extra digits were surgically removed and the horse went on to develop into a sound adult horse. You can read the full text of Bilateral Polydactyly in a Foal by Carstanjen, Abitbol, and Desbois online.

In evolutionary terms, polydactyls are what some people would call an atavism or a "throwback" to ancestors long ago. There are people who argue about this, of course. A book on my shelf is Hen's Teeth and Horses' Toes by Stephen J. Gould, which you might enjoy; it has some good illustrations of how the polydactyl forms in the limb.

Look very closely at this radiograph from the Florida Museum of Natural History and the collection of  Dr Bruce McFadden, Curator of Vertebrate Paleontology, and author of Fossil Horses: Systematics, Paleobiology and Evolution of the Family Equidae. (Used with permission, © University of Florida and Florida Museum of Natural History) 

Gould updated an old drawing of Dr. Marsh's from Scientific American in the 1800s to demonstrate two of the ways that a horse can grow an extra foot. The first way is for a true second lower limb to form. The second way is for the splint bone to turn into the limb, called the atavistic method. This drawing, from Gould's book, shows you the difference.

Are polydactyl horses truly rare? Unusual, yes. Dr. Robert Hunt at Hagyard Equine Medical Institute showed photos of polydactyls from his practice in Lexington, Kentucky in one of his presentations on foals at the AAEP's Foot Seminar in 2009.

While researching this article, I easily found a polydactyl horse for sale in Texas on CraigsList. (Should I have bought him? Is a polydactyl horse more or less valuable than a normal one?)

Horse described in the French paper, one of the few case studies documenting the condition.

Some of the better storyteller farriers have told me that they have had been asked to make shoes for the extra toes of polydactyls. I'd like to see a photo of that!

Would you get more work done if you had an extra finger? Yes, humans can have polydactyl traits as well. Perhaps my typing would improve if I had more fingers. This is the hand of a ten-year-old boy. (Wikimedia image uploaded by Drgnu23, a human podiatrist.)
I was imagining a horse show class for polydactyls and can just see them all lined up in the ring.

How often do you have to trim the extra hoof, is the next question, of course. Not being weightbearing, it mightn't grow very quickly, but what, if any, effect would feeding a hoof supplement have?

This "extra hoof" seen on a horse treated at Cornell University College of Veterinary Medicine might not even have been noticed if the horse's lower limb hadn't been clipped. (Image © Hoofcare Publishing for Michael Wildenstein)
Finally, the story of one of my favorite equine polydactyls: Norman Pentaquad (someone had a sense of humor) was a royally-bred son of the Thoroughbred sire Riverman; he was foaled in 1983 on a Kentucky farm. Not only was he small, he had an extra hoof dangling from his fetlock, which was surgically removed.

Norman wasn't much of a success on the track; his lifetime earnings only totaled $6,255, so he was soon exported to New Zealand to stand at stud. He was bought sight unseen, based on his bloodlines.

One of Norman's sons won both the Caulfield Cup and the Melbourne Cup. But in general, he was thought to be too small to sire runners, and his New Zealand owner was going to turn him out with the bush horses when an anonymous buyer suddenly made a quite high offer for him.

Norman was shipped to Australia and installed as the new polo stallion at Ellerston, the polo stud farm for Kerry Packer, then Australia's richest human. He went on to become the leading polo sire in the world. In 2010, Norman's offspring represented 11 percent of the horses that played for all nations in the semi finals of the Gold Cup.

I'd love to know how many legs they had among them.

• • • • •

More about polydactyls:

Ernest Hemingway was a fan of double-pawed cats and his house today in Key West is filled with the descendants of his original double-pawed cat. About half the cats have double digits. If you've never been there, I recommend it. The cats both run and over-run the place.

My friend Karin has a page on her web site about a polydactyl goat out in New Mexico, complete with radiograph and close-up photographs.

You can read a great story about Norman Pentaquad in the Australian newspaper, The Age.

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