Ergot rears its ugly head on the Prairie

Myrna MacDonald|May 11th, 2012|WCVM Today|Linked VAHS

 

A fungus that’s linked to human poisoning in the Middle Ages and even the 17th century Salem witch trials is affecting cattle in Western Canada today.

Claviceps purpurea is a fungus that mainly grows on rye, wheat, barley and triticale and causes ergot — a disease of grasses and cereal crops.

Ergot is most common in European countries and parts of North America where the climate is moist, cool and cloudy during the growing season. A telltale trait of the disease is the dark brown, purplish sclerotia (ergot bodies) that replace grain in the plants’ heads.

Besides affecting crop quality and yields, ergot produces alkaloids (organic compounds containing nitrogen) that can cause ergot poisoning in humans, cattle, swine and other mammals if they consume enough of the contaminated grain.

During the Middle Ages, ergot poisoning was common among rural Europeans who depended on rye crops for their daily bread. Today’s food safety standards have virtually eliminated the cases of human ergot poisoning — but it’s still a concern in livestock.

“Historically, we haven’t had a lot of problems with ergot in Saskatchewan,” says Dr. Barry Blakley, a toxicologist at the Western College of Veterinary Medicine (WCVM). “But in the last eight to 10 years, with the changing weather conditions and very moist spring months, conditions have been ideal for this fungus on the Prairies.”

The number of calls that Blakley receives about ergot poisoning in cattle has significantly increased in the past two years — especially in the past couple of months. Calls are mainly coming from producers and veterinarians in the western parts of Saskatchewan and Alberta.

Since ergot-contaminated grain receives low grades at the grain elevator, Blakley says some livestock producers are tempted to use affected grain for animal feed rather than pay extra for the grain to be cleaned.

“What they don’t realize is that even a small amount of ergot can cause major issues,” explains Blakley. The range of ergot contamination that can cause poisoning symptoms in cattle is between 0.1 and 0.3 per cent.

With continual exposure, cattle can develop the gangrenous symptoms of the disease where the ergot alkaloids cause constriction of blood vessels. When this occurs, the cow’s extremities — teats, ears, tail and feet — have restricted blood flow that can lead to gangrene.

“It’s similar to freezing where the body slows down the blood flow to the extremities in order to preserve the body’s core temperature. The same thing happens here . . . the feet or tail will basically slough off,” says Blakley. Animals must be euthanized in severe cases, but even mildly-affected cattle lose their market value.

In pregnant cattle, abortion or decreased milk production are two other potential effects of continual, low exposure to ergot-contaminated grain. “Even if the cow doesn’t abort her calf, her milk production may be affected and that will have an impact on her calf’s growth,” says Blakley.

A WCVM research team, including Blakley, has submitted a grant to further investigate ergot’s impact on pregnant cattle’s prolactin levels — the hormone that’s involved in milk production. “The gangrene symptoms are important, but the loss of milk production and the impact on the health of a producer’s calf crop may be even more significant from an economic standpoint.”

The increased incidence of ergot poisoning on the Prairies is also highlighting the need for specialized toxicological testing. Prairie Diagnostic Services, Saskatchewan’s veterinary laboratory, currently doesn’t have the equipment to test for ergot poisoning in submitted samples — but that may change in the future. PDS is seeking funding to purchase a liquid chromotograph mass spectrometer (LCMS) that will be used to identify a wide variety of organic chemicals including pesticides, antibiotics and mycotoxins such as ergot.

While gangrene is the most typical ergot-related symptom among cattle on the Prairies, high levels of exposure to the contaminated grain can also cause another disease form whose symptoms include convulsions, muscular trembling, stumbling and hyperexcitability in affected cattle. Animals rarely have both forms of the disease.

Similar symptoms used to be witnessed in human cases, and that has led some researchers to hypothesize that ergot poisoning was behind the bizarre behaviour exhibited by people who were accused of being witches in Salem, Mass., during the 1690s.

Blakley points out the central nervous system-affected variation of ergot poisoning is rarely seen in cattle, and if so, neurologic signs disappear once the contaminated feed is taken away since ergot is rapidly eliminated from the body.

Avoiding any use of ergot-contaminated grain is the best prevention, says Blakley. “Our impression is that the safe level of ergot in any feed is quite low — lower than what people may think.”