A herd health protocol will likely include vaccination of calves for blackleg, regardless of the area in which it is written. Blackleg affects cattle worldwide and is primarily caused by a bacterium, Clostridium chauvoei. This type of bacteria exists in an endospore which allows it to lie dormant for extended periods in the cow’s gastrointestinal tract, spleen and liver, as well as in soil. Endospores are extremely resistant to environmental conditions such as heat, drought, ultraviolet radiation and chemical disinfectants. The disease is always a threat due to the dormancy periods and resilience of the causative organism.
Significance of blackleg as a threat to cattle health is evidenced by it being listed as a discussion topic every year at the Texas A&M University Beef Cattle Short Course. During the 2013 event, the disease was discussed by Max Irsik, DVM, MAB of the University of Florida IFAS Extension. Information in this article was taken from Dr. Irsik’s presentation, as well as from University of Arkansas Division of Agriculture Bulletin No. FSA3073 prepared by Dr. Jeremy Powell, Associate Professor – Animal Science Veterinarian.
Infection Mechanisms and Symptons
“Blackleg is a very acute, non-contagious and highly fatal disease of skeletal and heart muscle in cattle,” states Irsik. “Death rates of infected cattle are near 100 percent. The disease is mainly seen in cattle from six months to two years of age. It infrequently affects cattle greater than two years of age, and occasional losses may be seen in adult cattle.”
“Blackleg infection begins when the susceptible animal ingests endospores,” says Powell. “The disease may be more prevalent on farms and ranches where soil has been recently moved or turned and around flooded areas where water has floated spores to the ground surface. Blackleg may also occur during drought when grass is very short, and cattle ingest spores from the soil during grazing.”
“Following ingestion, the organism may live in the gastrointestinal tract, spleen, and liver without causing any problem,” Irsik continues. “What causes the bacteria to proliferate is not entirely known, but it is 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, producing toxins that cause muscle death and, subsequently, animal death.”
Blackleg infected animals observed before death are depressed and show signs of lameness and swelling in the affected limb. Early in the disease process, body temperature may reach 106 degrees Fahrenheit, and the swollen area may be painful to the touch. Later in the disease process, the swelling becomes cold and is not painful to the touch. Often when the swollen area is touched, there is the perception of air under the skin. The time from the 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. Often, affected animals are found dead without displaying clinical signs.
Prevention and Treatment
Vaccination is the only way to effectively control blackleg. The first vaccination is usually administrated at 60 to 90 days of age or when calves are first processed. A booster dose of the bacterin should be repeated in four to six weeks or at weaning. In areas with a high disease incidence, additional vaccinations may be administered depending on the herd veterinarian’s recommendation. Most cattle producers use the multi-valent 2-way to 8-way clostridial bacterin. In addition to blackleg, multi-valent bacterins protect against other clostridial diseases such as tetanus, malignant edema, red water, black disease, enterotoxemia, overeating disease and botulism. Blackleg vaccines should be administered subcutaneously (under the skin) in the neck area. Read and follow all label instructions and withdrawal times for slaughter.
“Treatment for blackleg is usually futile; however, in the face of an outbreak, it is effective to vaccinate and administer procaine Penicillin G at the same time. The antibiotic will stop the proliferation of the bacteria and its associated toxin, allowing time for the vaccine or bacterin to stimulate protective immunity in the calf,” says Irsik.
“Carcass disposal should be done carefully after a blackleg outbreak occurs,” states Powell. “If possible, bury carcasses deeply where they lie. Do not drag carcasses across the pastures, contaminating more ground.”
Blackleg is a continual threat to the calf crop, if animals are not vaccinated. Even though bacterin is cheap and effective, the disease is seen on a yearly basis. The National Animal Health Monitoring System (NAHMS) reported in 1997 that only about 70 percent of all cattle operations vaccinated against blackleg. Although the vaccination percentage has greatly increased since that date, there are a few cattlemen that still fail to take necessary steps to prevent the disease.