During a drought, Arkansas cattle producers should be alert for potential herd health problems from a blackleg disease. Blackleg, a soilborne pathogen, is usually ingested by cattle as they graze on shorter and shorter forage.
While blackleg is an infectious disease, it's not a contagious disease. In other words, cattle that become infected won't directly transmit the disease to other cattle.
The spores that cause the disease enter the bloodstream and are deposited in muscle tissue throughout the animal's body. Spores lie dormant in the muscle tissue until stimulated to cause disease. It's only activated in a low oxygen environment such as damaged or bruised tissue.
Muscle tissue that has been damaged will have a compromised blood flow, so oxygen will not be as readily delivered to the affected tissue area. Therefore, any activity that causes bruising will promote the disease. Once this stimulating event occurs (transporting, handling, injection sites, rough/rigorous pasture activity), the spores germinate and multiply into the disease-causing bacteria.
Although blackleg has occurred in calves as young as two months, the disease generally affects animals between six months and two years. Rarely, losses may also be seen in adult cattle.
Blackleg generally affects well-conditioned, rapidly growing calves. It may be more prevalent on farms that have recently done excavation or in areas that have been flooded, which allows the spores to rise to the surface of the ground.
Typically, animals infected with this disease die rapidly without signs of illness.
However, clinical signs that may be noted early include lameness, loss of appetite, fever and depression. Animals die within 12 to 48 hours after contracting the disease. Although treatment usually fails, if attempted, appropriate doses of penicillin may prove helpful. If an animal does survive, it'll likely suffer from a permanent deformity.
It's virtually impossible to prevent contact with the infectious agent, so vaccination becomes the only way to effectively control this disease. It's generally recommended to vaccinate calves between two and three months of age. Before this period, calves should be protected through passive transfer of antibodies in the dam's colostrum.
A regular vaccination protocol should be followed around weaning. Calves should receive two doses of the vaccine during this period. The second dose should be administered three to six weeks following the first dose. Two vaccinations given in this manner provide the best protection.
If an outbreak of disease has occurred, a producer should contact his/her local veterinarian so that a proper diagnosis can be reached. The veterinarian will probably recommend that all animals receive immediate vaccination and follow-up boosters. Further losses may occur for a two-week period until the animals develop immunity against the disease.
Always be sure to read and follow the instructions on the label when using a vaccine. Blackleg vaccine should be administered under the skin in the neck area. The common blackleg vaccines are referred to as “seven-way” because they protect against other diseases such as malignant edema, black disease and enterotoxemia.
Carcass disposal should be done carefully after an outbreak of disease occurs. If possible, bury carcasses deeply where they lie, so that they will not be dragged across the pastures contaminating more ground.
Dr. Jeremy Powell is the Arkansas Extension Veterinarian.