Chestnut

The first thing to settle about chestnuts is which chestnut. Sweet chestnut (Castanea, the kind roasted in winter and sold jarred or vacuum-packed) is not toxic to dogs; the cooked, peeled kernel contains nothing harmful. Horse chestnut is a completely different tree, Aesculus, and it is toxic. In the US that genus includes the Ohio buckeye and the ornamental horse chestnut planted along streets and in parks, and the ASPCA lists Aesculus among the toxic plants. It contains aesculin. The nuts look enough alike that the safe answer for anything picked up outdoors is simply not to let your dog eat it. With true edible chestnuts, the risk is mechanical and caloric rather than chemical. The spiny bur, the hard outer shell and the bitter inner pellicle are not digestible, can lodge in the throat, and can cause an obstruction. A dog that swallows treats whole can get hung up on a peeled kernel by itself. Chestnuts are also unusual among nuts in being mostly starch, so they are carbohydrate- and calorie-dense; too many mean constipation, gas and weight gain. The way chestnuts usually reach an American table is worse than the plain nut: Thanksgiving stuffing and chestnut purée typically carry butter, salt, sausage, and often onion, which is genuinely toxic, and marrons glacés and canned sweetened chestnuts are mostly sugar. If you want to share one, keep it plain: fully cooked, shell and inner skin removed, no salt, no sugar, no seasoning, and cut into pieces small enough that swallowing them whole is not an option. One to two peeled cooked chestnuts is a reasonable occasional amount for a medium dog, less for a small one. Start with a single piece the first time and see how the stomach handles it. Call your veterinarian if your dog swallowed shells or a whole bur, if it ate a nut off the ground and you cannot rule out a buckeye or horse chestnut, or if chestnuts are followed by repeated vomiting, straining without producing stool for more than a day or two, or abdominal pain. In those situations do not try to make your dog vomit at home; check with the clinic first.