| Bob Larson, DVM, PhD Reproductive physiologist and Epidemiologist Beef Cattle Institute Kansas State University RLarson@vet.k-state.edu |
Blackleg and other clostridial diseases are caused by a family of bacteria that can release large amounts of toxins that vary between the specific clostridial organisms. Different species of clostridial bacteria tend to cause disease in different ages of cattle, and the most common clostridial diseases of young calves are blackleg, clostridial enterotoxemia, and occasionally, tetanus.
Blackleg is caused by Clostridia chauvoei that enters cattle through the digestive tract and can be found in many tissues of healthy animals. The disease is created when the bacteria multiply rapidly in muscle and releases large quantities of a fatal toxin. Muscle trauma or bruising from handling, trucking, or normal animal interactions may be required for the bacteria to have a suitable environment to multiply rapidly, but the exact requirements for disease onset is not known.
Blackleg is most common in young calves up to 12 months of age, with animals more than 1 to 2 years of age rarely being affected. The disease attacks very rapidly and in many cases a dead calf is the first indication of a problem. Blackleg (like other clostridial diseases) is not considered a contagious disease, in that the disease does not pass directly from one calf to another – rather it is from soil to an animal. An outbreak may appear contagious in that a number of animals can be affected in a short period of time, usually following a soil disturbance. Any event that disturbs the soil, such as flooding, pond repair, bulldozer work, laying water pipe, etc, can initiate an outbreak of blackleg disease in pastures with heavy loads of blackleg organisms. Although vaccination is not 100% successful at protecting calves from blackleg disease (especially in young calves), vaccination will decrease the number of calves that are susceptible to the organism.
Clostridium perfringens or enterotoxemia is typically a disease of young calves. Most commonly, death following the onset of disease is so rapid that the first sign of a problem is to find a dead calf. Affected calves are typically suckling cows with high milk production and are often the healthiest, fastest-growing calves. Because the germ normally lives in the gut of healthy calves, two things must happen for the organism to multiply rapidly and produce large amounts of the toxin. First, the bacteria need an abundance of carbohydrates (which is present in milk), and secondly, the intestinal tract motility must be at least partially slowed (which occurs following a large meal). Following a large milk meal, high levels of toxin can be produced and death can occur rapidly.
Tetanus is caused by Clostridium tetani and cattle are not as susceptible as many other species – but deaths due to tetanus are occasionally seen. The organism can enter a wound and produce toxins that cause death. Many commercially available clostridial “Blackleg” vaccines do not include a component for protection against tetanus. Vaccines for cattle that provide protection against tetanus are available, and are commonly used when cattle are castrated with elastic bands as this method of castration is associated with some tetanus deaths.
Because the vaccine is fairly effective, a program where calves are initially vaccinated at 2 to 3 months of age with subsequent revaccination is recommended.