Fighting a fatal fungus.

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Horse breeders can be blindsided by toxic plant infestations. An article by Darek Gondor.

Horse breeders like to keep a close eye on herd health because it’s far more effective and efficient to prevent disease than to treat it. So in 1999, when one Ontario standardbred farm reported unusually high numbers of sick newborn foals, researchers were called in along with the attending veterinarian to look into the problem. Bob Wright, a veterinary scientist with the Ontario Ministry of Agriculture and Food (OMAF), accompanied a private practitioner in the investigation. The Animal Health Labo-ratory at the University of Guelph had already determined there was no evidence of a virus or bacterial infection.

This made the most likely culprit a mycotoxin produced by a plant fungus. Although the farm’s hay wasn’t directly associated with the problem, the team soon discovered that the mares were consuming much of their straw bedding because their hay was of poor quality. “We suspected the bedding was contami-nated with something called ergot alkaloids, which act much like fescue toxicity, a well-known type of toxin,” says Wright. “Once the bedding was replaced, the mares delivered normally and foals were born healthy.”

Suspicions on the rise He found the ergot alkaloids were pro-duced by fungi growing on the cereal rye straw that was used as bedding. These same fungi were blamed for many human deaths in the Middle Ages, when people consumed contaminated rye flour. “It was a breakthrough when we linked the problem to the ergot alkaloids found in the straw,” says Wright. “We suspected they were acting like the chemicals that cause dif-ficult births and foal death, as seen in fescue toxicity.” Normally, a mare’s late pregnancy is marked by rising concentrations of the hormones prolactin (involved in milk pro-duction) and progesterone. They prepare the mare and foal for birth.

In ergot-affected mares, however, both hormones are sup-pressed, leading to thickened placentas. “When this occurs during foaling, it means a long and difficult delivery where the foal may suffocate on its way out,” says Wright. Along with difficult births, mares often fail to produce milk. In 2001, after more cases of unexplained foal sickness, Wright decided to determine whether ergot alkaloid toxicity was a prob-lem in Ontario. He took blood samples to analyze hormone levels. He also tested hay and straw and collected placentas from 340 mares on six farms. The results were promising for horse owners.

“Fortunately, we found very low levels of ergot alkaloids on the test farms,” he says. Safety at home Wright is now identifying the kinds of ergot alkaloids present in his samples. If he can connect certain types of hay and the toxins, preventive measures can be adopted to keep horses from being exposed to infected plants in the future.

Other researchers involved in this project are Dan Kenney and Tony Van Dreumel of the Ontario Veterinary College and Jim Bren-demuehl and Morrie Craig of Oregon State University. The research was sponsored by the Ontario Horse Racing Industry Association.