We know that contaminated feed can cause serious problems for horses, ranging from colic and cardiac problems to neurologic issues and death. For instance, researchers recently documented a case in which feed contaminated with trichothecene mycotoxins caused signs of bone marrow cell proliferation suppression, severe bleeding, and hair loss in horses that consumed it.
During a presentation at the 2015 American College of Veterinary Internal Medicine Forum, held June 4-6 in Indianapolis, Indiana, Rachel Liepman, DVM, a resident in internal medicine at The Ohio State University Veterinary Medical Center, shared what she and colleagues recently learned about trichothecene ingestion’s impact on four American Quarter Horses.
Liepman said the index case—an 11-year-old mare—presented to a clinic with lethargy, acute perineal edema (fluid swelling in the perineal area, beneath the tail), hematochezia (bloody stools), fever, patchy alopecia (hair loss), and petechiation (small purple spots on mucous membranes). The mare’s bloodwork showed severe panleukopenia (a decreased white blood cell count), thrombocytopenia (decreased numbers of circulating blood platelets), and a prolonged prothrombin time (how long it takes blood to clot). Additionally, when veterinarians evaluated her bone marrow, they found profound myeloid hypoplasia (decreased white blood cell production) and megakaryocytic hypoplasia (decreased production of megakaryocytes, which produce platelets), Liepman said.
In collecting the mare’s history, Liepman said the veterinarians learned that she, along with other horses, had recently received a new batch of hay. This initially caused feed aversion and later some drooling, she said, and the team further learned that the hay had been improperly cured (dried) during production.
[image imageid="5132" includeTitle="false" includeSummary="false"]Trichothecene mycotoxins also caused petechiation (small purple spots on mucous membranes).[/image]
On initial presentation, the mare also had septic peritonitis (an inflammation of the peritoneum, or the membrane lining the abdomen), Liepman said, most likely secondary to severe immunosuppression and gut irritation from the toxins. The team treated her aggressively with anti-inflammatories, antibiotics, and blood transfusions. After eight days, however, her condition deteriorated and she was euthanized.
Subsequently, veterinarians ran blood tests on the other horses at the mare’s home facility that had shared the contaminated hay source. Liepman said one older horse—a 19-year-old gelding—exhibited milder petechiation and patchy alopecia, but had similar bloodwork and bone marrow findings as the mare and was referred to the clinic. That horse recovered following treatment with a single blood transfusion, anti-inflammatories, and antibiotics, she said—a result Liepman said was notable in itself.
“Despite severe bloodwork and bone marrow abnormalities, the second case survived, and his white blood cell count and platelets returned to normal, albeit eventually,” she said. “Most vets would look at that bloodwork and deem the cases hopeless.”
The remaining horses—two mares aged 6 and 8 years—both recovered with conservative management including removing the hay from their diet and property and supplementing them with antioxidants.
Liepman said toxicology testing showed high levels of mycotoxins in the hay, including 1,627 parts per billion of the T-2 toxin and 1.1 parts per million of vomitoxin. Both substances are in the trichothecene mycotoxin group.
“Trichothecenes have radiomimetic properties (like radiation toxicity) and generally target bone marrow cell precursors, with T-2 being the most toxic—actually, one of the most potent toxins known,” Liepman explained.
“The myelosuppression in these cases was consistent with trichothecene intoxication, which is poorly documented both in horses and from a forage source,” Liepman said. “Reports typically mention these toxins in association with cereal grains. Most toxicologists didn’t believe me when I said this was a forage contamination—that how rare it is!”
And although not all horses can recover from severe disease, “the clinical course of these cases suggests that spontaneous recovery is possible following severe myelosuppression due to trichothecene intoxication in horses,” she noted.
So how can owners protect their horses from ingesting trichothecene from forage? The main way is to ensure the hay you choose is produced properly.