Black Leg
When diseases disappear from the farm we forget about them. Sometimes they disappear because we have eliminated them entirely, but more often it is due to management techniques. This can lead us into a false sense of security. No feet problem recently? Maybe we go a little longer between foot trims and foot baths. No scours? Maybe our strict colostrum protocol relaxes. No mastitis? Maybe we don’t need to clean the teat dip cup each milking. Unfortunately, each time we slip, we open the door for these conditions to return. In the examples above, you might see small changes, just little reminders to refocus on good management. However, if what has passed from recent memory is the last time you had a case of Blackleg, and so you have gone a few years without vaccinating, the reminder can be swift and harsh. In the past year within our practice area we have seen both beef and dairy herds affected, all cases occurring in unvaccinated animals. The case fatality rate in blackleg approaches 100 per cent in most cases, and for this reason it can be a cause of severe financial loss to cattle producers.
Clostridium chauvoei is a bacterium that lives in soil, all soil. It thrives in warm, wet soil, but can remain quiet for years. Outbreaks can occur out of nowhere but are often associated with flooding (high rainfall), excavation, and other soil disturbances. Animals are most often exposed by ingesting the spores, which then pass into the blood stream and localize in muscle and other sites. When the spores become activated the toxin spreads quickly and most often hit the “best calf” you have. The most easily recognized form is a very swollen leg that has small air bubbles trapped within the tissue- they can feel like rice crispy cereal under the skin. Less-easy to identify forms include infections to the heart, lungs, and diaphragm. In these cases, you might notice a calf with pneumonia-like symptoms, and before the day is done it has died. When the disease occurs, it is not uncommon for a number of animals to be affected within a few days. It mostly affects cattle five to six months to two years of age that are rapidly growing on a high plane of nutrition. It hits hard, fast, and the first case is often just the tip of the iceberg.
From the time the first swelling appears, you may only have 12 hours to react and attempt treatment. To have any chance of survival, penicillin is the best choice for antibiotics. Adding anti-inflammatory treatments can help reduce pain and inflammation. If your calf dies, don’t wait for a second animal. Call the veterinary clinic for a necropsy. If it was a limb swollen, the muscle will literally be blackened inside (see photos below). If it was possibly pneumonia, we need to distinguish this from the cardiac form of Blackleg. Early disease identification and vaccination of the herd is the only way to prevent what could be significant losses.
Tasvax 8 is our current black leg vaccine, and is relatively cheap compared to other vaccines. For about $1 a dose, you can prevent this disease from decimating your herd. Ideally, each calf should get two doses four to six weeks apart like any killed vaccine, although giving one dose has shown short term protection for calves going out on grass. After that, boosters after 6 months age and yearly will provide adequate immunity. It is safe to give to pregnant cows, even if they have never had the vaccine before. The veterinarians at McGregor Veterinary Services will help you develop a vaccination schedule that works for you and your herd. If you have any questions about Blackleg, or other vaccination programs for your herd, please get in touch with our office. We are here to help you achieve your herd health and productivity goals!
Additional Examples:
Sometimes only one part of the muscle is affected, sometimes the entire limb. Right is an example of a severe case. Note the air bubbles in the layer right under the skin. This is where gas gets caught and can be felt on presentation.
Here we see the importance of TasVax before castration. This photo was taken days post castration. TasVax was given at the time of castration, but as this was the first dose it was not enough to protect from this infection. It is always best to have the first dose in before castastration, and then use that time to give a booster dose.