As detailed in a 1999 Western Producer article, a Dawson Creek, B.C., producer lost 75 calves and cows to blackleg. Another producer lost about one-third of his herd to blackleg following vitamin A injections.
Now that summer is here, it is important to take note of this disease. It can cause devastating losses in warm weather. Calves and yearlings on pasture are particularly at risk.
Though Clostridium chauvei is well recognized as the cause of blackleg, it is still unclear how it invades the body. It is presumed that the bacterium is consumed, passes through the intestinal wall and enters the bloodstream. Some veterinarians believe it remains in the body as a permanent resident and constant threat.
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Clostridial bacteria flourish in anaerobic conditions – tissues with little oxygen. It readily grows in damaged tissue that has a compromised blood supply. Muscle tissue that has been injured with a bruise or by an injection is particularly inviting.
Blackleg kills cattle rapidly. The severe signs are caused by the release of toxins from the bacteria. Most animals are found dead with no signs of illness. If they are identified early, they will exhibit high fevers and lack of appetite.
Animals suffering from blackleg become extremely depressed and may develop swelling in the muscles of the shoulder, hip, flank or back. As the disease progresses, these swellings enlarge and become soft to the touch. When pressed, a crackling sound can be heard. This is caused by the accumulation of gas under the skin, which is released by the growing bacteria.
Cattle that die from blackleg decompose rapidly. They are bloated, their legs are extended, and a frothy, bloody discharge is often evident at their nostrils and anuses. Discoloured serum and gas escape if the swollen muscles are cut open. The discharge can contaminate the ground around the carcass and pass the infection to others.
Because of the rapid progression and severity of a blackleg infection, a veterinarian should be called in to make an accurate diagnosis as soon as possible if it is suspected. Any delay could be costly.
It is thought to be almost impossible to prevent cattle from picking up the clostridial bacterium. Producers who say that it has never been seen in their district before are relying on history to protect their cattle. New outbreaks are seen each year in areas where the disease has never been reported.
In the Dawson Creek area, producers had not seen cases for years so they decided not to vaccinate their animals. For at least 15 herds, it was a bad decision.
Traditionally, calves were vaccinated at branding time. Since many producers don’t brand, that opportunity has been lost. Ideally, calves should be vaccinated between one and three months of age and again at six months of age. Alternatively, a blackleg program can be instituted at weaning by giving one vaccine and a second one four to six weeks later. These calves should be vaccinated next at a year of age.
A mixed multivalent vaccine is commonly used for blackleg. It provides protection against several clostridial diseases including blackleg and malignant edema. Vaccines should be administered under the skin in the neck region.
If an outbreak occurs, all cattle on the property should be immediately vaccinated.
Because it takes a few weeks for cattle to develop full immunity, they won’t necessarily be spared, but in the long run, more will survive. If the disease is identified early, cattle may respond to immediate treatment with penicillin.
