That’s a tough question, Liz. Buckeye (Aesculus spp.) is a member of the Hippocastanaceae family, and contains a toxic component known as aesculin. When ingested, buckeye can potentially produce significant GI irritation, dilated pupils and severe central nervous system depression, possibly leading to coma. In some cases, however, the opposite—central nervous system excitement—is seen.
Concentration of the toxin can vary from tree to tree, and even from one buckeye nut to another—so it is difficult to determine the number of nuts that could be problematic. Because of this, we advise that you do not allow your dog to consume any amount.