As autumn rolls around, pastures become depleted as grass and plant growth slows prior to going dormant for winter. So, it’s not surprising that this time of year can also bring an increase in reports of horses becoming ill from eating something they shouldn’t have.

Karyn Bischoff, DVM, MS, Dipl. ABVT, a diagnostic toxicologist at Cornell University’s New York State Animal Health Diagnostic Center, said it does appear there are more suspected cases of poison plant ingestion in late summer and autumn, but also says these are difficult to diagnose.

"Plant ingestions over time can cause chronic disease, so by the time the horse is noticeably sick, the plant is gone because it was all eaten, it’s out of season, or the horses were moved to another stable or pasture after exposure," Bischoff explained.

She added that plant toxins can be difficult to find in the body as the particular toxin are sometimes not known, there are no good tests for it, or the toxin has metabolized and gone before the horse presents clinical signs of serious illness