How to Diagnose Blackleg in Cattle

The first sign of blackleg in cattle is often a dead bovine. This fatal disease usually affects animals between the age of 4 months and up to 2 years, with blackleg seldom occurring in cattle older than 2. Beef breeds are more prone to blackleg than dairy cows. One odd aspect of blackleg is that it most often afflicts apparently healthy, strong animals, rather than those in lesser condition. Perhaps the easiest way to diagnose the condition yourself is by observing the legs in a suddenly sick animal. Leg muscles may turn dark from inflammation -- the reason why the disease got its nickname. However, the only way to make a definite diagnosis is via a necropsy performed by a veterinarian. Fortunately, vaccinating your young stock against the cause of blackleg protects your herd.

Blackleg generally results from infection by the bacteria Clostridium chauvoei. Other types of clostridium bacteria also can cause the disease. Clostridium chauvoei spores are commonly found in pasture soils. Once a susceptible bovine consumes the bacteria, it passes into the animal's bloodstream and heads to the muscles.

Blackleg comes on suddenly, generally with no prior warning that anything is amiss in the animal. Symptoms include lameness, with swelling developing in the animal's hips, back, neck, shoulders and other areas. These swellings start out as relatively minor, but continue to grow. Initially, the swelling feels hot and is obviously painful to the animal when touched. As the swelling increases, the affected area turns cold. The animal appears depressed, stops eating and may run a fever when symptoms first occur, but the temperature may return to normal as the situation worsens. As the end nears, the animal may begin shaking and fall down. The animal dies within 48 hours of becoming symptomatic. Rarely, an animal receiving large amounts of the correct antibiotics administered by a veterinarian before the disease progresses will survive.

Avoid the heartbreak of blackleg by initially vaccinating calves against clostridium at the age of 3 months, followed by a second inoculation within four weeks. Each animal should receive an annual booster a year later. If you have an affected animal on your farm, the Merck Veterinary Manual recommends treating all asymptomatic cattle in the herd with penicillin for two weeks as a preventive measure.