Blackleg

Blackleg is a highly fatal disease of cattle. It is most commonly seen in the warmer months of the year and most commonly affects cattle aged 6 months to 2 years of age. Calves are often found dead with little signs of struggle, or are observed suddenly lame and die quietly in 12 to 24 hrs, they bloat quickly and develop gas under the skin.

The disease is caused by a bacteria which is found on the ground. Spores are ingested, the bacteria then get into the bloodstream and travel to the muscles where they lodge and remain virtually undetectable.

When the disease occurs it usually affects a number of animals over a few days. The disease is initiated by trauma to the muscles where the spores are lodged, the muscle damage stimulates the bacteria to multiply rapidly, calves are lame, running a high temperature, and the affected area is hot and painful. As the bacteria proliferate a powerful toxin is produced which rapidly kills the surrounding tissue, producing gas and causing more muscle damage and further activation of bacteria. The calves are now quite depressed and the affected area is cold, painless and may have gas under the skin. The bacteria continue to proliferate, the toxin is absorbed into the bloodstream and the calves die soon after from toxic shock.

Usually 10% to 20% of the group will be affected but some losses may exceed 50%. It is common to observe that the biggest and healthiest animals are affected first. Treatment of affected calves is usually unsuccessful due to the rapid progression of the disease, however high doses of penicillin in the very early stages of the disease may help.

Adequate vaccination is very effective in preventing blackleg. In most situations, the common practice of vaccinating calves at weaning, again one month later and again at 12 months is adequate. However calves will not be fully protected until 2 weeks after the second injection. In areas where blackleg has occurred recently calves should be fully vaccinated before weaning, this may mean giving the first injection at 4 weeks of age and another 3-4 weeks later. An extra shot at 6 months of age is also recommended in high risk areas.

 



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