Horsetails are perennial, non-flowering, erect plants which are composed of more than 30 species in the genus, belonging to the Equisetaceae family. This fern-like, spore-producing plant is generally found in moist-to-wet areas across Europe and North America. It is also sometimes a contaminate in hay.
Horsetail Toxic Components
The plant contains several toxic compounds but its toxicity is believed to be due to the presence of the enzyme thiaminase, the alkalid nicotine and piperidine alkaloids.
Thiaminase is an enzyme that destroys thiamine, an important B vitamin that is needed for proper brain function.
Symptoms of poisoning in horses develop slowly, and begin with unthrifty appearance, weight loss without loss in appetite, diarrhea, and slight incoordination. Without treatment, signs will progress to more extreme--leading to balance problems and loss of control of muscle movement, eventually leading to death in approximately 1-2 weeks.
Control of horsetail is not easy. The plant has rhizomes that, when cut up by mechanical removal, can distribute the plant to other areas. Draining excess water from marshy areas may help. The ideal method of control is to cut horsetails when they are young and growing, before maturity and spore distribution.