Blackleg In Cattle

Blackleg is a peracute, non-contagious, and highly fatal (nearly 100%) disease of skeletal and heart muscle of cattle. It is mainly seen in cattle from 6 months to 2 years of age. It infrequently affects cattle greater than 2 years of age.

The infective agent: Clostridium chauvoei, a bacterium, is the primary causative agent. This class of bacteria exists in a spore form in the presence of oxygen. Because in the spore form it is resistant to environmental changes and disinfectants it can survive in the soil for years.

The disease process: The soil-born Blackleg organism enters the animal by the ingestion of contaminated feedstuffs. Following ingestion the organism may live in the gastrointestinal tract, spleen, and liver without causing any problem. What causes the bacteria to proliferate is not entirely known but it’s most likely a result of muscle bruising associated with handling, and shipping. There is also a recognized increased incidence in Blackleg when calves are on a high plane of nutrition and are experiencing rapid growth rates. When conditions in the animal are right the bacteria enter into a rapid proliferation phase resulting in toxins being produced that cause muscle death and subsequently the death of the animal.

Clinical signs: Animals observed before death are depressed, show signs of lameness and swelling in the affected limb. Early in the disease process the body temperature may reach 106° F and the swollen area may be painful to the touch. Later on in the disease process the swelling becomes cold and non-painful to the touch. Often times when the swollen area is palpated there is the perception of air under the skin (crepitation). From beginning of clinical signs to death ranges from 12 to 36 hours. Some affected animals may not show any lameness or limb swelling but the diaphragm, heart, or tongue may be involved. Many times affected animals are found dead without displaying clinical signs.

Treatment: Visit your veterinarian immediately. Treatment is usually futile. In the face of an outbreak it is effective to vaccinate and administer procaine penicillin g at the same time. The penicillin will stop the proliferation of Clostridium chauvoei allowing time for the bacterin to produce immunity in the calf.

Prevention: Blackleg bacterin is effective. Most operations use the multi-valent Clostridial bacterin (2-way to 8-way). The first vaccination usually occurs at about 60 days of age and will be repeated at either 4 weeks pre-weaning or at weaning. In areas with a high disease incidence a booster vaccination will be administered depending on the local veterinarian’s recommendation. Even though the Blackleg bacterin is cheap and historically effective the disease is seen on a yearly basis. The 1997 NAHMS reports that only about 70% of all cattle operations vaccinate against Blackleg.

Take home message:
1. The Blackleg organism, Clostridium chauvoei, can live in the soil for years in its spore form.
2. Blackleg is still a threat to the unvaccinated calf.
3. Blackleg is easily prevented by proper administration of Clostridial chauvoei bacterin in the healthy calf.
4. The carcass of an animal that dies of Blackleg should be disposed of to prevent the further premise contamination.

Key suggestions:
1. Have your veterinarian establish an appropriate herd health protocol.
2. Read and follow all label instructions and withdrawal times for slaughter.
3. Give all vaccines subcutaneous if there is an option according to the label.

CattleNetwork.com