Blackleg prevention
What is blackleg?
Blackleg is an acute, usually fatal disease of cattle and sheep, caused by the production of toxins by anaerobic soil-dwelling bacteria called clostridia. These bacteria survive in soil normally as spores, and when they enter the body they may proliferate in anaerobic (air-free) conditions, producing toxins which kill muscle tissue (necrosis) producing gas in the process. This results in darkened areas of muscle with pockets of gas throughout the lesion (see Figure 1) and is usually rapidly fatal. Some blackleg cases present as lameness or areas of swelling, but most are found dead. Very rapid decomposition and significant gas accumulation under the skin is often a feature of clostridial deaths (but not diagnostic).
How is it diagnosed?
Your vet may be able to diagnose it by a clinical examination, or may refer carcasses to your nearest Regional Veterinary Laboratory for post mortem and diagnostic tests.
Figure 1: This photo from the Department’s Regional Veterinary Laboratories, shows a cross section of the iliopsoas (fillet) muscle from a 5-month-old-calf showing dry gangrenous black muscle, overlying normal unaffected muscle. The causative agent, Clostridium chauvoei, was detected in this lesion using a fluorescent antibody test. The small cavities within the dark & dry area of affected muscle are pockets of gas produced by the bacteria which gives rise to the crackling texture that is evident when you touch the overlying skin of an affected area – often compared feeling as though there were froth or ‘suds’ under the skin.
Clostridium chauvoei bacteria can survive for decades, perhaps centuries, as highly stable spores. Outbreaks have been associated with flooding and other forms of soil disturbance such as tillage, drainage, etc can trigger outbreaks by bringing spores to the surface. Indeed some farmers will be aware that some areas of their farm are ‘blackleg hotspots’.
What should I do to prevent it on my farm?
The disease is common, and the best control is prevention by vaccination. Successful vaccination requires the selection of a suitable vaccine (broad spectrum multivalent clostridial vaccines provide a wider range of protection against blackleg and prevent other diseases like tetanus also) and correct storage and administration, as per the data sheet that will be enclosed with the product.
Please contact your private veterinary practitioner regarding correct Blackleg vaccination procedure for your farm.