A few weeks ago, a stable in the Urbana, Ill., area received a shipment of wood shavings to bed its stalls. Little did anyone know that within this batch of shavings from a furniture manufacturer was black walnut–which contains a toxin that causes horses to become lame within 24 to 48 hours.

According to Elysia Schaefer, DVM, an equine surgery resident at the University of Illinois Veterinary Teaching Hospital in Urbana, who 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."

"It can take as little as 5% black walnut in a batch of shavings to cause laminitis in a horse," Schaefer said.

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 should be considered.

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," Schaefer said. She also mentioned that the fresher the shavings, the more likely they are to harm the horse.

Kate, the owner of a horse diagnosed with black walnut laminitis, said she checked on her Quarter Horse early one morning, and 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.

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, Schaefer mentioned 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 can also be used during 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.–Ashley Mitek, University of Illinois College of Veterinary Medicine


An archive of Pet Columns from the University of Illinois College of Veterinary Medicine is available online at www.cvm.uiuc.edu/petcolumns. Requests for reprints of this article may be directed to Mandy Barth, mandyb@uiuc.edu.