Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Poisoned Through Their Hooves


Pet Column for the week of December 3, 2007


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ashley Mitek
Information Specialist

A few weeks ago, a local stable received a shipment of wood shavings to bed its stalls, as is routine for most horse operations. Little did anyone know that within this batch of shavings from a furniture manufacturer was a toxin that mysteriously causes horses to become lame within 24 to 48 hours.

The culprit is black walnut. If furniture is made from this type of wood, the shavings will inevitably find their way into horse stalls if the furniture manufacturer contracts for services with a horse barn.

According to Dr. Elysia Schaefer, an equine surgery resident at the University of Illinois Veterinary Teaching Hospital in Urbana who has treated affected horses, "The exact toxin that causes the laminitis is unknown, but it is absorbed through the hoof wall and causes inflammation, leading to pain." Technically speaking, laminitis is a painful inflammation of a structure in the hoof called the lamina, which causes a horse to become lame.

"It can take as little as five percent black walnut in a batch of shavings to cause laminitis in a horse," says Dr. Schaefer. Although finding black walnut in shavings used for horse stalls is rare these days, if several horses in a large barn become lame simultaneously, black walnut laminitis becomes an increasing suspicion.

Once black walnut laminitis is suspected, the most important thing to do is to remove the horse from the stall as quickly as possible. "The longer the horse has been exposed to the toxic shavings, the more severe the long-term effects may be," states Dr. Schaefer. She also mentions that the fresher the shavings, the more likely they are to harm the horse.

"His legs were swollen and he refused to walk forward," says Kate, the owner of a horse diagnosed with black walnut laminitis. When she checked on her quarter horse early one morning, she was very concerned by his awkward stance and swollen limbs. She immediately loaded him in the trailer and drove to the equine clinic at the Veterinary Teaching Hospital where veterinarians were able to begin treatment for laminitis.

Typical treatment of a horse with black walnut laminitis is the same as for a horse that has laminitis from a different cause. Veterinarians begin by taking radiographs, or x-rays, to examine the bones in the horse's hoof to make sure they have not rotated out of position.

To reduce swelling, laminitic horses usually have their legs cold hosed a few times a day, and also receive some type of anti-inflammatory medication. To alleviate pressure on the horse's hoof, Dr. Schaefer mentions that these horses frequently will be placed in a sand stall or have styrofoam pads placed beneath their hooves. A new commercially-marketed product, "Soft Rides," act as tennis shoes for horses, and also aid in the recovery process.

The only way to confirm that black walnut is present in bedding is through a laboratory analysis. The wood shavings in this case were sent to a botanist in Wisconsin to determine if black walnut was present.

If you suspect your horse has made contact with black walnut shavings, remove it from the stall and call your local veterinarian immediately.