Blackleg is still around?
By Michael Fisher
CSU Area Livestock Extension Agent
How many of you have ever heard a cattle producer say that he/she was going to save money by not vaccinating for blackleg this year? It always surprises me to hear this. A greater surprise is to discover how many people think that blackleg is a disease that is under control and nearly eradicated. Just last week, I heard of a rancher losing several purchased heifers to this savage disease. He had been told at the point of purchase that the heifers "had all their shots." After he began losing animals, his vet called the seller and asked what he had used to vaccinate for blackleg. The response was, "Blackleg, that doesn't exist anymore. That was one of those diseases that my dad had to worry about."
If you raise cattle or sheep, it is a disease that you need to worry about. It will affect sheep of any age. Typically, cattle producers consider it to be a replacement heifer disease because it normally only infects cattle between the ages of 6 months and 2 years. However, calves as young as 6 weeks and cows as old as 12 years have been documented victims of the disease. Usually, they will be your fast growing, high performance animals that are really doing well. Still, the disease can strike cattle of any age. Blackleg vaccines are available and are usually very effective at preventing your cattle from breaking with blackleg.
So what causes blackleg? It is one of the clostridial diseases. There are more than 60 types of Clostridium bacteria. Not all of the clostridial types cause diseases; however, many members of this bacterial family cause diseases specific to the clostridial type. Some examples are malignant edema, sord, black disease, red water and several types of enterotoxemia. In the case of blackleg, Clostridium chauvoei is the culprit.
The Cl. chauvoei bacteria have three important characteristics that have maintained their survival and deadly success since their discovery in medieval times. First, they have developed the ability to survive extreme environmental conditions by developing into highly resistant spores. As spores, the bacterium can live in soil for many years, waiting for its opportunity to attack. Secondly, Cl. chauvoei only multiply in the absence of oxygen. This is a very effective ability for a disease that attacks the muscular skeletal system. The third characteristic is the release of gas and toxins. As the bacterium multiplies in the animal's muscle tissue, toxins and gas are released causing damage to the muscle.
I have known cattle producers who have moved cattle herds because a neighbor had a blackleg outbreak. They wanted to protect their herd from the dreaded disease and did not want their cows within breathing distance of the blackleg infected herd. However, the disease is not transmitted from sick animals to healthy animals. The animal's environment is the source for transmission of blackleg. The previously mentioned spores lay in wait for the opportunity to come in contact with an open wound or to be ingested by a grazing animal. Ingested bacteria will invade the body via small puncture wounds in the animal's digestive tract. It is important to note that land that has had cattle or sheep on it before, probably has Cl. chauvoei spores in it. There are certain conditions that may cause the disease to become active in a pasture that previously had seemed free of the disease. Fresh disturbances of the soil such as tilling, gopher or prairie dog damage and erosion from heavy rains can all increase your herd's risk of an outbreak. Additionally, flooding may force the spores up out of saturated soil and provide a greater opportunity for animal contact.
Once the bacterium has taken up residence within the host animal, it rapidly begins to multiply and excrete gasses. Research has shown several signs and symptoms for the disease. These include lameness, loss of appetite, depression, rapid breathing, fever and swelling. The swelling is characteristically in the hip, back, neck, chest and shoulder. It should feel hot to the touch and will present as being very painful to the animal. In severe cases the swelling may be crepitant. In other words, it may crackle as though you have just pressed against a bag of rice crispies.
Probably the most common first sign of the disease is to find a dead animal. The disease can kill within 12 hours of infection and usually does so by hour 48. Your veterinarian can implement an aggressive penicillin treatment plan to try to save sick animals. This has been shown to work in some cases. This is more effective when you start early in an outbreak. It is not uncommon for prime blackleg conditions to affect an area for a period of 10 days, leading to continually finding sick and/or dead animals over a two week time period.
Those animals that die need to be dealt with immediately. You will want to pick them up and carry them out of the pasture as opposed to dragging them out on a chain. The entire carcass is a breeding ground and major shedding source for the Cl. chauvoei bacteria and becomes your herd's number one risk factor. The carcass should be burned completely or covered with quick lime and buried deeply, where predators, scavengers and normal rainfall will not be reintroducing the carcass and its spores to your herd.
As previously mentioned, there are several members in the clostridial family. Many of them effect the muscular system and are generically accused as being part of the blackleg group. When you purchase a blackleg vaccine it may be effective against multiple bacteria. Usually, what we refer to as a clostridial 7-way will protect against Cl. chauvoei (blackleg), Cl. septicum (malignant edema), Cl. sordelli (sord disease), Cl. novyi (black disease) and three types of Cl. perfringens (enterotoxemia). You need to make sure that the vaccine that you are using will protect against your bacterial problem.
I can be reached at the Yuma County Extension office, 970-332-4151 or by e-mail at email@example.com.