Technical Abstract: Horses are relatively selective grazers and generally are poisoned less frequently than other livestock. However there are exceptions. Some poisonous plants are palatable to horses and exposed horses readily eat them. Most equine poisonings occur as result to toxic plants contaminating feeds. Most horses readily ingest toxic plants that are included in hay or processed feed. This acceptance and social competitions for feed contribute to most clinical poisonings. As plant induced toxicity in horses can result in irreversible disease and antidotes are rare, plant-induced diseases are often devastating for both work and companions animals. Knowledge of which plants are toxic and when horses are likely to be poisoned will help reduce losses and ensure animal health and safety. In this series differ toxic plants that are likely to damage horses are discussed. The series are divided by body system affected with emphasis on neurotoxic and hepatotoxic plants that are potential problems in the western United States.