Blackleg incidents prompt vaccination reminders

Several animals died of blackleg on a farm in the Melville, Sask., area in mid-August.

The incident prompted veterinarian Zachary Johnson to remind producers about the importance and effectiveness of vaccination against the fatal illness.

“That producer in particular hadn’t vaccinated within the last five years for blackleg,” said Johnson about the case.

“So we had a bit of discussion about cost per head and cost of finding the disease once it actually has hit and how the numbers just don’t make sense to not vaccinate, basically.”

The vaccine costs 70 to 85 cents per head per year. That cost compared to potential loss of several animals — and usually more than one animal is affected before the illness is either noticed or diagnosed — and the economics are clear.

“Awareness needs to change,” said Johnson, who owns and operates the Melville Veterinary Clinic.

“I’ve come across many producers that feel that you do a vaccine once every five years and you’ll be covered. But I think with the severity of the disease once it actually hits compared to the cost of the vaccine, it doesn’t make sense to not do it every year or at least every other year.

“My ideal protocol would be to vaccinate them every year at the same time you do your respiratory vaccines for your mature herd.”

The vaccine takes 10 to 14 days to provide immunity and is administered under the skin.

Blackleg is caused by a soil-borne pathogen called clostridium chauvoei, which is ingested by cattle when they graze. Spring, when grass is short, and fall, when the tastiest grass can also be short or scarce, are the most common times for a blackleg occurrence. Soil disturbance such as flooding can also increase the chances.

The pathogen spores lie dormant in the body until activated by tissue damage or bruising of the animal’s muscle from things such as transportation or handling. Then the spores quickly multiply and produce a toxin that kills the animal.

“It’s usually sudden and sometimes, if you’re lucky, you see it before they are just found dead or recumbent,” Johnson said. “Most often you’ll just see them as down and unable to rise, or severe lameness and death occurs shortly after and it’s usually fairly fast.”

Cattle can appear fine in the morning and be dead by evening, according to producer accounts. Severe lameness, initial fever and depression are the main symptoms, as well as swellings that occur often at the hip, shoulder or chest.

A “bubble wrap” feeling when pressing on the animal’s skin is a further sign, an effect produced by the toxic spores.

The chance of effective cure is low, in part because the illness develops so quickly and is often in late stages by the time the problem is identified.

Blackleg is often thought to be the greatest threat to young calves but cattle as old as 12 years have been known to get it. Compounding the problem, it often affects well-nourished and healthy cattle.

Johnson confirmed blackleg on the Melville-area farm through a post-mortem on one animal.

“It has a pretty distinct smell. Not many people are going to go stick their nose in it, but when you cut it open it does have a potent smell” somewhat like rancid butter,” he said.

The illness also affects sheep, often following injury such as shearing cuts or castration, according to the Merck Veterinary Manual. It advises that the carcasses of animals that die of blackleg should be burned or deeply buried to limit spore contamination of the soil.


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