Q: After Christmas each year, we recycle our tree as filler for a cross-country jump. Last year I noticed our pony was nibbling at the needles, so I removed it from the field. Now I’m wondering if that was necessary. Could an old Christmas tree (we typically get Fraser firs) be toxic to horses? — Name withheld by request
A: Pines, spruces and firs are the most common sources for Christmas trees, depending on the area of the country. While pine needles are toxic to cattle when eaten in quantity, they are not known to be toxic to horses. Similarly, spruces and firs are not poisonous. Horses that chew on the bark of these trees may experience mild irritation to the mouth because the bark contains various oils that can be irritating. Horses on a good plane of nutrition are not likely to be affected if they nibble on a few needles. In contrast, red maple and its hybrids, yew, rhododendron and black walnut are among the trees and shrubs that are most toxic to horses.
Another holiday plant your horse might have access to is the poinsettia. Contrary to popular belief, poinsettias are not really poisonous to horses, dogs or cats. If ingested poinsettias may cause some salivation and perhaps diarrhea, depending on how much was eaten by a horse. This seems highly unlikely, as it would take eating pounds of the poinsettias to cause any signs of poisoning.
Anthony P. Knight, BVSc, MS, DACVIM
College of Veterinary Medicine & Biomedical Sciences