The soil around my old property is largely sand and gravel. It drains quickly, making it the perfect for this variety of horsetail. Other varieties grow in more marshy areas. If the plant is dried into hay the toxin may have a greater effect than in the fresh plant. The toxin in this plant destroys the Vitamin B in the horse's blood.

Symptoms of Horsetail poisoning are:

• weakness
• stumbling
• arrhythmia of increased pulse

• death
• irritability

Resources: Indiana Plants Poisonous to Livestock and Pets Cooperative Extension Service, Purdue University
OMAFRA: Poisoning of Horses by Plants, Author: Penny Lawlis - Animal Care Inspector/OMAFRA
If you suspect poisoning from any plant or substance call your veterinarian immediately.