How can you protect your horses from equisetum - a weed toxic to horses? How can you prevent horsetail from poisoning your horses? Find out.

Toxic Plant in Utah Hay Blamed for 9 Horse Deaths

Equisetum toxicity in horses

Nine horses died in Utah after eating hay contaminated with a toxic plant less than two weeks ago.

Equisetum or "horsetail" is a fern like-plant toxic to horses. There are more than 15 species of horsetail so it's not unique to Utah.
Equisetum or “horsetail” is fernlike and toxic to horses. It has two types of stems, one that is unfertile (above) and one that is fertile (right).

Veterinarians confirm the Wellington-area horses ate hay baled unknowingly with equisetum. As a result, the hay masked the less palatable toxic plant. Commonly called “horsetail,” horses are highly susceptible to illness or death due to equisetum toxicity when consumed in large amounts.

Horsetail contains an enzyme that prevents the body from producing thiamine (vitamin B1). Thiamine plays a vital role in the horse’s central and peripheral nervous system. In other words, thiamine deficiency causes neurologic damage, which may lead to recumbency, and the horse’s eventual death, if untreated.

Veterinarians treated the Carbon County farm’s herd for thiamine deficiency, but for some, it was too late.

The Utah Department of Agriculture and Food wasn’t notified regarding the horses’ contaminated hay deaths. Doug Perry the state ag agency’s public information officer says, “if it’s not commercial feed then there is no inspection or regulation.” Therefore, he adds, there is no reporting requirement unless horses die after eating hay purchased commercially.

Horsetail is toxic to horses and has two types of stems. This one is fertile with a cone-like structure containing spores, not seeds.
Fertile horsetail stems have a cone-like structure containing spores. Horsetail has 15+ species found worldwide.

Horsetail poisoning treatment

Once horsetail poisoning is suspected, horses should no longer eat equisetum contaminated hay.

Veterinarians treat equisetum toxicity in horses with thiamine hydrochloride intravenously for several days. Antibiotic, fluids, and electrolytes may be necessary to prevent infection and dehydration. After, veterinarians may prescribe oral thiamine or thiamine injections.

Good farm management practices can help prevent this and other poisonous plants from growing in your horse pastures.

Before growing horse hay, consider investing in a crop scout. A crop scout inspects fields for various pests and weeds in order to increase hay yield and quality. This will keep your horses happy and healthier longer.