Knowledge is Power. It's not always easy to diagnose, but toxicity in horses, or poisoning can be difficult to determine, and sometimes is even harder to treat. Knowing what types of trees, plants, shrubs, weeds, and even bedding your horse could be around is the first step in preventing major health problems. Although horse's are not supposed to consume these toxic forages, it happens. Given plenty of good quality forages and access to healthy feed, a typical horse will not eat poisonous materials. That being said, horses don't read the manuals! Even consuming large amounts of certain dry or wilted tree leaves can become toxic. Know what you are feeding, and what your horse has access to.
These helpful documents listed below as pdf's are great resources.
Common Poisonous Shrubs and Trees- 1 page Chart from Equus Magazine August 2007
Plants Poisonous or Harmful to Horses in North Central United States by Univ. or Minn. Ext. -48 pages
Guide to Toxic Plants in Forages WS-37 by Purdue Univ. Ext - 28 pages - great color pictures!
Poisonous Plants - Horse Nutrition Bulletin 762-00 by Ohio State Univ. Ext. - 17 pages
Poisonous Pasture Weeds - w additional links - 6 pages
Vegatation that is Toxic to Horses -by Spring Creek Horse Rescue - 10 pages
Poisoning of Horses by Plants - by Penny Lawlis, OMAFRA - 6 pages
Poisonous Plants and Equine by Utah State University Ext. - 9 pages
Toxicology - plants to horses - 2 page summary - handout from Equine Open House by Wayne SWCD
Various Symptoms of Poisoning in Horses - 2 page summary- handout from Equine Open House by W SWCD