Blackleg is a disease that most cattle producers are relatively familiar with, if for no other reason than the ‘blackleg’ vaccine is probably the most commonly administered vaccination by cattle producers. And this for good reason, because for those producers that may have elected to forgo vaccination and unfortunately experienced the disease firsthand as a result, blackleg can be truly unforgettable. The disease frequently affects the biggest, fastest growing calves and renders them acutely dead in the majority of cases.
Blackleg is the common term for infection with a gram positive bacteria called Clostridium chauvoei. Cl. chauvoei forms spores that are highly resistant to disinfectants and can survive in the soil for years. This means that cattle producers cannot reasonably prevent exposure of their livestock to the organism. Incidences of exposure can be very localized, even to a single field and may be related to periods of flooding or excavation of the soil. Exposure is most common during the warmer months of the year. It is thought that the organism enters the animal’s body through the gastrointestinal tract. Infection with the organism produces severe inflammation and death of muscle tissue. The growth of the bacteria in the muscle tissue results in significant toxin production and build-up in the animal’s system ending in death.
Fast growing calves 6 months to two years of age are at highest risk. It is uncommon that mature cows and bulls are affected with the disease. Most producers recognize that they have a problem when they find one or multiple animals dead. This is simply because most animals die within 12-48 hours of infection. A classic post-mortem sign of blackleg infection is gas accumulation under the skin producing a ‘bubble wrap’ type feel often over the back or hindquarters. If the muscle is incised it is found to be dark or bruised in color and may have a metallic appearance on the cut surface. Prior to death, calves will show signs of severe lameness and swelling of the limb over the area of damaged muscle. If calves are diagnosed with blackleg before acute death ensues, the treatment of choice is high doses of penicillin G. Unfortunately, treatment is frequently unsuccessful.
Thankfully, however, vaccination for the disease is very effective and inexpensive. Maternal antibody generally provides protection to calves for the first 3-4 months of life, however, it is recommended to vaccinate calves initially at 60 days of age in an effort to immunize those few calves with poor maternal antibody protection. Calves are then vaccinated 30 days prior to weaning and are boostered at weaning. Cattle are then boostered annually. Vaccination of mature animals is generally only necessary if a farm is experiencing frequent cases. Rarely do producers have outbreaks in properly vaccinated herds. Therefore, using the cheap, yet effective vaccination to prevent such a deadly disease provides significant economic advantage and is highly recommended to all producers.
Darren Loula, DVM, is a large animal veterinarian at Fair Grove Vet Service in Fair Grove, Mo.
