Contaminated Alfalfa hay kills 14 horses in the US

Contaminated Alfalfa Hay Kills 14 Horses in the US

Veterinarians called in to assist owners at the Red Ridge Ranch Riding Stable in Wisconsin, have reported 14 horses lost from the consumption of contaminated Alfalfa hay. They noted a further 100 horses at the ranch are now stabilised and showing signs of recovery. Analysis of the ranch’s winter Alfalfa hay reserves showed the forage to be contaminated with fragments of the blister beetle, most likely to have occurred during the cutting process.

Why is the Blister Beetle so feared?

The Blister Beetle is a member of the Meloidae family, it lives in Alfalfa and secretes a blistering agent when under threat. The largest genus, Epicauta, contains many species that release a toxic substance called Cantharidin, which is dangerous to animals and especially, horses.

Even the smallest fragments contain the poison Cantharidin and studies have shown as little as four to six grams of ingested beetle can be fatal to horses. Dead beetles and dead beetle parts retain their toxicity and it is not affected by drying or heat.

Where are Blister Beetles Found?

There are approximately 7,500 species of blister beetle found worldwide, although not all are poisonous. The genus Epicauta Vittata is toxic and remains the most well-studied subspecies, commonly found in America and Canada. Other subspecies of the Meloidae family are less well known, however many show vivid stripes and colours highlighting their toxicity to potential predators.

Toxic species of blister beetle are found globally, from the United States and Europe, to South Africa and parts of Asia. In addition to the Epicauta Vittata, common subspecies include; the striped Blister Beetle, the black Blister Beetle (E. Pennsylvanica), the Margined Blister Beetle (E. pestifera), and the Three-Striped Blister Beetle (E. Lemniscata), as well as E. Fabricii, E. Occidentalis, and E. Temexa.

Signs of Cantharidin Toxicity in Horses

According to the American Association of Equine Practitioners, many vets and owners often misdiagnose the poisoning in its early stages. Symptoms usually present three to 18-hours after ingestion and initially requires the urgent removal of all remaining toxin from the stomach.

Symptoms include:

  • The horse ‘dunking’ its head into water in an effort to relieve the pain.

  • Horses may have fever, diarrhea, decreased appetite, or seem depressed and lethargic.

  • Endotoxic shock and colic: This is usually a result of mucosal damage and from the migration of normal intestinal bacteria.

  • Salivation and anorexia: This results from vesicle (blister) formation and erosions in mouth and tongue.

  • A toxic line: A purple-blue line that forms on the gums around the base of the incisor teeth, this usually indicates some degree of endotoxemia.

  • Watery faeces or bloody stools which is a result of abraded and deteriorating gastrointestinal mucosa.

  • Cardiac arrhythmias which are often from electrolyte abnormalities (or hypocalcemia) or damage to the heart muscle itself (myocardium).

  • Hematuria (bloody urine): Evidence of renal damage or maybe from ureter, bladder or urethral mucosa damage.

  • The Thumps also called synchronous diaphragmatic flutter which can be seen as a rhythmic contraction of the abdominal musculature. It occurs because of hypocalcemia and your horse may appear to have various degrees of hiccups.

  • Bloodwork may reveal low levels of magnesium (hypomagnesemia) and calcium (hypocalcemia), increased packed cell volume (PCV) wherein protein levels in the blood will indicate dehydration, increased blood urea nitrogen and creatinine indicating renal damage and dehydration. Depending on what stage of the syndrome your horse is in, your veterinarian may also observe a transient, or short-lived, hyperglycemia.


Worryingly, there is no known antidote for Cantharidin. Current treatment options remain entirely supportive and can include intravenous fluids to combat dehydration.

Activated charcoal and mineral oil may be administered to help evacuate toxins from the gastrointestinal tract and delay potential absorption, while gastric protectants may decrease gastrointestinal discomfort and colic.

Steps for Reducing Blister Beetle Contamination in Alfalfa/Hay