Cases of blackleg often increase when animals are turned out or moved to new pastures, so farmers need to be aware of the signs so that action can be taken to prevent further disease
What is Blackleg?
Blackleg is a highly fatal disease of muscle caused by the bacterium Clostridium chauvoei. Infection begins when bacterial spores are eaten (usually as result of eating soil, but occasionally from contaminated feed). These spores enter the bloodstream and travel to organs and tissues throughout the body (particularly muscles). They remain dormant until a trigger (usually an injury) stimulates them. The trigger reduces blood flow and thus the supply of oxygen to the tissues. In the absence of oxygen the bacteria multiply and produce a local infection. As they grow, the bacteria produce poisons that destroy the surrounding tissues. This damage shows as the characteristic black muscle with gas. The poisons do not stay in the muscle but enter the bloodstream, resulting in animal that very rapidly goes downhill and dies. The disease is most commonly seen in calves between six months and two years of age, but occasional cases are seen in adults and it can occur in younger animals (particularly if they have not had sufficient colostrum). Disease is definitely more common in animals that are growing well
Clinical Signs
- Lameness may be seen before death if you’re lucky
- In a few cases the first sign seen is tongue and throat swelling with the tongue protruding
- However, the most common sign is sudden death in an otherwise apparently normal animal
- The carcass often looks like a much less fresh carcass, with bloating and gas under the skin
- Bloody discharge from the nose, mouth and other body openings are also seen
Diagnosis
- A post mortem is essential to diagnose blackleg. Many other diseases cause sudden death and need to be ruled out. The most important of these is anthrax, which must be ruled out before a PM is done
- The changes in the muscle are characteristic, but the extent of the damage can vary considerably. Some cases have black oozing muscle throughout the hindquarters, others have much smaller areas of damage which may not involve the limbs at all.
- It is worth getting further lab tests done to confirm it is Cl. chauvoei as other clostridial bacteria can cause similar muscle damage Don’t do a PM on farm. Opening the carcass can liberate bacteria which will form spores to contaminate the ground and subsequently infect other cattle.
Treatment
- In very early cases very high doses of penicillin may prevent death, but the extent of muscle damage means that in most cases this will not be economic
Prevention
As the bacteria are present in the soil, preventing access to soil by not grazing freshly sown pastures with youngstock can reduce the risk, but vaccination is really the only effective means of controlling blackleg. The main choice is between vaccination against Cl. chauvoei alone or with vaccines that are effective against other clostridial disease. Ask your vet for advice
With clostridial vaccines, like all vaccines, care should be taken to follow the manufacturers’ instructions. The best protection is a two-dose course followed by annual revaccination. Other regimes can be effective but check with your vet before using these. Vaccination takes 10-14 days to become effective, so it’s best to vaccinate before a problem occurs or a risk period is encountered.