Q: I know we should never use black walnut shavings as stall bedding because even small amounts can cause laminitis. But are there any other kinds of wood, like cherry, we also need to avoid? How can we know our bedding is safe to use?
A: Wood shavings are a popular type of stall bedding, but horse owners need to know the source because a few tree species can be toxic. The best known is black walnut (Juglans nigra L.), a common hardwood tree native to the eastern United States from the Great Plains to the East Coast and from the Great Lakes region to the Gulf of Mexico. Black walnut trees have also been planted outside of their native range, particularly in the Pacific Northwest. Although the lowest amount that is toxic has not been established, we know that a horse who stands on a shavings mixture with as little as 10 percent black walnut, by weight, will develop painful laminitis within 24 to 48 hours. Black walnut shavings are a distinctive chocolate brown color, which stands out against the lighter woods typically used in beddings.
Several other species of tree are best avoided for bedding, too many to list in detail here. But as a general rule, don't use wood shavings from trees that have any parts that are toxic when ingested. For example, both the native and imported varieties of yews (Taxus spp.) are extremely toxic---as little as eight ounces of leaves can be deadly to a horse, so even the shavings need to be kept away at all costs. I also recommend steering clear of shavings made from maples (Aceraceae family) in case any toxic leaves are accidentally bagged with the wood. In the Midwest, horses bedded on shavings from the simarouba tree can develop blisters and lesions in the oral cavity, around the nose, lips, anus and on the tongue within 48 hours of exposure.
The best way to be sure your bedding is safe is to purchase shavings from a reputable supplier who is familiar with horses and livestock. Do not buy bedding from tree trimmers or yard maintenance businesses because their employees may not be as knowledgeable about the tree species that can harm horses. Also avoid any byproducts from a carpentry shop because the lumber may have been treated with potentially dangerous additives and preservatives. Material that was intended for use as mulch should not be used as bedding.
As a side note, a study from Denmark observed that horses kept on straw spent much more time lying down and sleeping than did those kept on shavings---but of course with straw, you also have the additional worry about the horses eating the bedding as well as the added manual effort in cleanup. As always, frequent cleanup is critical to reduce ammonia levels.
If you have specific questions about toxic materials, you can always check with your veterinarian, your nearest university equine health center or the American Society for the Prevention of Cruelty to Animals (ASPCA) 24-Hour Animal Poison Control Center hotline at 888-426-4435 or visit www.aspca.org/Pet-care/poison-control.aspx.
Jim Latham, DVM
Mill Creek Veterinary Service
Fort Collins, Colorado
This article first appeared in EQUUS issue #431.