Blackleg, also known as black quarter and quarter ill, is a rapidly fatal bacterial disease of sheep and cattle. Cattle with blackleg may seem completely fine in the morning and be dead by evening. This disease most often strikes cattle that are six to twenty-four months old, but cattle of any age can be effected.
The organism that causes blackleg, Clostridium Chauvoei, is an anaerobic bacterium that can live in the soil as a spore for years or even decades. When ingested, the bacterial spores may enter the bloodstream and find their way into the muscles. Once in the muscles, these spores may remain dormant for many years until something occurs (such as a bruise or other minor injury) that causes conditions favorable to their growth. Once the bacteria become active, they secrete a toxin that kills the surrounding muscle tissue - and then the bacteria proliferate rapidly in the dead tissue. Large sections of the animals body essentially rot within a few hours and the toxins released from the decaying tissue cause the animal to go into shock, which soon progresses to death.
Cattle that are affected with blackleg may lose interest in food, run a high fever and suddenly appear to be lame. One area of the body (often a leg or shoulder) may appear to be swollen. If pressure is applied to the swollen area, a crackling sound may be heard due to gas pockets which are formed in the decaying tissue. On autopsy, the swollen area will be dark colored, contain gas bubbles and have a foul odor.
Most cattle with blackleg will die within twenty-four to forty-eight hours in spite of treatment. Occasionally, if the disease is caught in its very earliest stages, massive doses of penicillin may stop the disease and allow the animal to recover. Cattle that recover from blackleg may be permanently lame due to the severe muscle damage this disease causes.
If an animal is known to have died of blackleg its carcass should not be opened. Opening the carcass can liberate bacterial spores which will contaminate the premises and subsequently infect other cattle. The recommended disposal method for these carcasses is either incineration or deep burial.
The best treatment for blackleg is vaccination before the disease occurs. Most cattle in the United States are vaccinated with a 4-way or 7-way vaccine which is protective against a number of clostridial diseases, including blackleg. Blackleg is seldom a problem among vaccinated cattle - but it can be a severe problem in unvaccinated herds.