Acorns Could be to Blame for French Horses' Deaths

At least 10 horses have died in northwest France from poisoning after consuming acorns,  according to a treating veterinarian.

The horses had consumed sufficient quantities of acorns to potentially result in tannin toxicity, said Hélène Lemoine, DVM, equine veterinarian in Saint Lô, Normandy, France. Tannin is present in the leaves, bark, and acorns of oak trees and affects the intestinal tract and the kidneys.

“None of the affected horses survived,” Lemoine told The Horse. “As soon as they showed signs of hemorrhagic diarrhea death followed very quickly, usually before we could even arrive on site to examine the horse.”

Strong winds and rain in the region have caused significant quantities of acorns—including unripe acorns, which are more toxic—to fall from the trees recently, often into pastures, Lemoine said. According to the Western Animal and Environmental Anti-Poison Center (CAPAE) in Nantes, France, it takes approximately 3 kg (6.6 lbs) of acorns to poison a 500 kilogram (1,100 pound) horse.

Although post-mortem examinations were not carried out, the cases were very “typical” for tannin poisoning, Lemoine said. All the horses—most of which were mares—had colic associated with bloody diarrhea, and all the owners reported that their horses had eaten acorns.

Different kinds of oak trees have different levels of tannin, according to CAPAE. The deciduous pedunculate oak and two varieties of sessile oak are considered to be the primary poisonous species in France which were likely responsible for the deaths of the horses in Normandy.

However, any acorn tree could be dangerous for a horse, and the source of the danger still hasn’t been confirmed, said George Burrows, DVM, PhD, professor emeritus at Oklahoma State University and author of Toxic Plants of North America. “We aren’t even sure that it’s the tannin that’s responsible for these effects in horses,” he said.

The horses in this report were located in Europe, but horses throughout the world can be prone to death from acorn consumption, Burrows said. However, some horses tolerate acorns better than others, for reasons that are yet understood.

Acorn-related illness usually affects the digestive tract and kidneys in cattle, but in horses, it seems to be limited to the digestive tract alone, Burrows said.

Usually, horses will not eat acorns if they have other, preferable food sources like plenty of grass or good-quality hay, Lemoine and Burrows concurred.

Lemoine recommended horses be kept in pastures free of oak trees, or where oak trees are fenced off so their acorns fall where horses cannot reach them. If horses do have potential access to acorns, ensure they have plenty of good grass, hay, and/or grains to dissuade them from seeking other food sources.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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