Blackleg

What is blackleg

Blackleg in cattle is a severe and often fatal disease caused by the bacterium Clostridium chauvoei, which is naturally present in the soil and the intestines of healthy animals. It primarily affects healthy, fast-growing young cattle between 6 months and 2 years of age but can occasionally occur in older animals.

The bacteria enter the body through ingestion or wounds and settle in various organs and tissues, where they remain dormant. They are activated when an injury occurs, reducing blood flow and oxygen supply to the affected area. In this oxygen-deprived environment, the bacteria multiply and produce toxins that destroy surrounding tissues. These toxins enter the bloodstream, causing the animal to become acutely ill and often results in rapid death.

Blackleg can occur year-round but is more prevalent during hot, humid weather or sudden cold snaps. It is particularly common in fertile soils and swampy areas or where there is an abundance of lush green feed, where increased carbohydrate load enhances the growth of the bacteria.

Symptoms of blackleg

Sudden death (often the first sign noticed)
Swelling, especially in the large muscles (legs, shoulders, neck)
Lameness
High fever (though affected animals may die too quickly to exhibit this)
Depression and refusal to eat.
Gas under the skin, making a crackling sound when touched (due to gas produced by the bacteria)

Prevention and management

Vaccination

Clostridial vaccines (often referred to as 5-in-1 or 7-in-1 vaccines) are highly effective in preventing blackleg.
For maximum protection of young calves, it is best to vaccinate pregnant cows 2–6 weeks before calving so that the calf can receive antibodies via colostrum.
For protection of calves from unvaccinated cows, vaccination is recommended typically at 2 to 3 months of age, with a booster 4–6 weeks later.
Annual boosters are often given to cattle, especially in high-risk areas.
For new stock, vaccination procedures should be introduced as for normal stock. If vaccination history is unknown, give a sensitising dose then booster 4–6 weeks later.

Carcass management

Dispose of dead animals properly to reduce contamination. If possible, bury carcasses deeply or burn where they lie, do not drag carcasses across the ground to prevent the bacteria from spreading and persisting in the topsoil and infecting other animals.

Environmental management

Minimize soil disturbance in areas where cattle are grazing, as this can expose dormant bacteria.

Treatment

Unfortunately, blackleg is almost always fatal, and treatment is generally not successful once symptoms appear. However, in rare early cases:

Antibiotics, such as penicillin, may help if administered very early, muscle loss will still occur.
Supportive care (fluids, anti-inflammatories) can be used, but prevention through vaccination is the most effective strategy.

Early detection and prompt action are crucial, but prevention is the best approach through routine vaccination.

Biosecurity obligation

If you are experiencing large losses and suspect it could be blackleg, please contact Biosecurity Queensland on 13 25 23 or the Emergency Animal Disease Hotline on 1800 675 888.

Local contacts

Biosecurity Queensland: Donna Weber, Senior Veterinarian Officer, mobile 0499 757 076, email donna.weber@daf.qld.gov.au

Department of Primary Industries and Regional Development Western Australia: phone 08 9368 333

Northern Territory Regional Livestock Biosecurity offices:

Katherine: 08 8973 9767
Darwin: 08 8999 2033
Tennant Creek: 08 8962 4492
Alice Springs: 08 8951 8125