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Poisonious Plants, Toxic to Horses - "Yellow Star Thistle"
Eating yellow star thistle and Russian knapweed brings on nigropallidal encephalomalacia, commonly called chewing disease.
Horses eat the plant over an extended period of time before symptoms appear.
The ingested toxins actually cause a softening of parts of the brain and once symptoms appear, the animal will almost certainly die.
The horse will not be able to eat or drink, although he may attempt to do so.
He may chew food only to spit it out when he cannot swallow, often acting as if something is caught in his throat.
Symptoms resemble the early onset of rabies, so you should consider rabies also as a possibility and not go reaching into the horse's mouth to look for obstructions.
- The horse may chew without having anything in its mouth
- move his tongue and lips in unusual fashions
- yawn frequently and assume unusual postures such as head hanging or pushing against solid objects.
Yellow Star Thistle causes a disease that damages the brain and prevents the horse from eating, there is no recovery.
Clinical experiments using poisoned horse's fed through stomach tubes have shown that even after extended periods of time, affected horses will not regain the ability to swallow.