BASICS
Yellow star thistle poisoning, also known as “chewing disease,” is a devastating disease caused by prolonged ingestion of yellow star thistle or Russian knapweed, resulting in degeneration of specific basal nuclei and the extrapyramidal system
- Access to hay or pasture containing yellow star thistle (Centaurea solstitialis) or Russian knapweed (Centaurea repens) for at least a month
- Toxicity produced when horses eat 50–200% of their bodyweight of the thistles, resulting in necrosis of the substantia nigra and globus pallidus
- Repin is the most abundant constituent isolated from these plants, and is a leading suspect for causing equine nigropallidal encephalomalacia. It has been shown to reduce cellular glutathione and increase reactive oxygen species
- Dopaminergic neurons in the basal nuclei may be more susceptible to oxidative stress
- Clinical signs appear suddenly in horses once they have consumed 50–200% of their bodyweight of the poisonous plants
- Paralysis of the lips and tongue present early in the course of the disease result in the horse being unable to eat
- Reduced jaw tone, tongue protrusion, and hypertonicity of the facial and upper lip musculature are also frequently observed. Other reported clinical signs include severe depression, with affected horses carrying their heads low
- Ultimately, poisoned animals are unable to eat, become weak and emaciated, and eventually die of starvation
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FOLLOW-UP
MISCELLANEOUS