Use Caution When Storing Antifreeze and Other Products Containing Ethylene Glycol Around Horses

For most horse owners, antifreeze poisoning stays comfortably distant in the realm of detective novels, fictional television shows, or news stories detailing neighborhood feuds. In a recent report, however, veterinarians in Romania described accidental antifreeze poisoning in 39 horses.^*

The primary component of antifreeze is ethylene glycol, a sweet but colorless and odorless syrupy liquid. While ethylene glycol has low toxicity, it is broken down in the body into four organic acids: glycoaldehyde, glycolic acid, glyoxylic acid, and oxalic acid, all metabolites that suppress oxidative metabolism. Because of this, ethylene glycol is considered extremely toxic and represents an important cause of intentional and accidental poisonings worldwide. Toxicity causes central nervous system dysfunction, cardiovascular compromise, and kidney failure. Depending on the amount of ethylene glycol ingested, death is possible.

All mammals are vulnerable to ethylene glycol poisoning, yet sensitivity differs among species. Humans and cats, for example, are especially sensitive to the effects of ethylene glycol. Exactly how horses respond to ethylene glycol poisoning has not been well documented.

In a recent report, researchers described antifreeze toxicity in 39 horses housed at a private facility. Caretakers found the horses depressed and slightly ataxic. Once on the scene, veterinarians also noted sweating, increased heart rate, abdominal pain, and decreased gastrointestinal sounds in all four quadrants. They administered fluids and ethanol to the horses with the hope of minimizing the production of toxic metabolites. Swift treatment increases the chances of a successful outcome.

Thirty-four horses recovered after the initial therapy, but five horses continued to show signs of toxicosis, preferred to lie down, and developed laminitis. These five horses were referred to a clinic for supportive care, with special emphasis placed on reducing anatomical changes of the hoof and related structures. All horses were discharged 10 days after admission with no lingering aftereffects.

Upon examination of the surroundings, caretakers found the horses’ water source contaminated with ethylene glycol. The flow-through water system had been inadvertently connected to the drainage tube of a nearby heating system, leading water laced with ethylene glycol to be mixed with the drinking water. Caretakers speculate the drinking water had been contaminated for approximately 18 hours before signs of toxicosis were observed.

Aside from this case report, only one other mention of ethylene glycol poisoning in a horse has been archived in scientific literature.^** In that case, a seven-year-old Dutch Warmblood gelding had ingested an antifreeze product with the primary health concern compromised liver function. Treatment for this horse centered on provision of intravenous fluids and ethanol, and the horse recovered and developed no further problems.

Steps have been taken to make ethylene glycol less appealing to animals, including the addition of a bitter compound, such as denatonium benzoate. This serves as a nontoxic deterrent in many countries, including the United States, United Kingdom, and Canada. Although several states in the United States have made the addition of bittering agent mandatory, attempts to pass national legislation requiring addition of these preventives to antifreeze and coolant products have failed, according to Congressional reports.⁺

 To reduce the likelihood of accidental ingestion on the farm, store antifreeze, coolants, brake fluid, industrial solvents, and other fluids containing ethylene glycol in out-of-the-way locations, far from horses, dogs, cats, and other animals. Further, stay on top of vehicle maintenance. If a leak from a motor vehicle or farm equipment occurs, take the necessary steps to repair it and quickly clean up any puddles created by the leak, using an absorbent material like cat litter or sawdust. Then, dispose of the contaminated absorbent material.

^*Daradics, Zs., D, Bungărdean, A.F. Lupsan, M. Popescu, O. Bulmez, V. Ciulu-Angelescu, V.F. Chelaru, I. Morar, M. Mircean, C. Cătoi, M.A. Tripon, and C.M. Crecan. 2025. Ethylene glycol toxicosis in 39 sport horses following ingestion of contaminated water: A case report. Journal of Equine Veterinary Science:105343.

 ^**Swor, T.M., P. Aubry, E.D. Murphey, M.T. Hines, R.G. Gant, and P.A. Talcott. 2002. Acute ethylene glycol toxicosis in a horse. Equine Veterinary Education 14(5):234-239.

 ⁺U.S. Senate, 109th Congress, First session, S, 1110, the engine coolant and bittering agent act of 2005; hearing before the Subcommittee on Consumer Affairs, Product Safety, Washington: Government Printing Office, 2005.