Blackleg: A Preventable Disease of Cattle
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Introduction
Blackleg is a preventable, soilborne disease of both cattle and sheep that producers need to be concerned about. It is caused by an anaerobic, soilborne bacterium (Clostridium chauvoei) and is almost always lethal. Animals are usually found deceased and exhibit swelling under the skin which “crackles” when pushing down on it.
Blackleg vaccines, usually 7- and 8-way products, are widely available and are very effective at preventing livestock from contracting this deadly disease.
Animals Affected
Blackleg is a non-contagious but highly fatal disease, with nearly 100% death loss. Animals found alive can be given high doses of penicillin, but outcomes are poor. It is a peracute infection, meaning it is very severe and of very short duration.
It will infect sheep of any age, but it mainly affects cattle from six months to two years of age. However, in rare cases, it may affect calves as young as six weeks and cows as old as 12 years of age. Sadly, this disease usually infects fast-growing, high-performance animals that are growing well.
Cause of Blackleg
Most cases of blackleg are caused by the anaerobic, spore forming bacteria, Clostridium chauvoei. Very few cases are caused by Clostridium septicum. Blackleg gets its name because it typically infects the rear leg muscle, causing it to turn a darkened or black color.
There are more than 60 types of Clostridium bacteria. Clostridial organisms are anaerobes, which means they like to live and grow where there is no oxygen. There are several diseases in cattle caused by different Clostridial species. Some examples are malignant edema (Cl. Septicum), black disease or infectious hepatitis (Cl. novyi), and several types of enterotoxemia (Cl. perfringens types C and D).
Clostridium bacteria 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 strike and infect a host.
The Disease Process
Blackleg is not contagious. The source for transmission is the clostridia bacterium spores waiting in the soil 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. Animals also can eat feed with contaminated with spores.
As previously stated, blackleg usually attacks livestock younger than two years of age. The soilborne blackleg organism enters the animal through ingestion of contaminated forage. Following ingestion, the organism may live in the gastrointestinal tract, spleen and liver without causing any problem.
It is not entirely understood what causes the bacteria to proliferate, but one theory is muscle bruising associated with handling and shipping may be a major cause. Once the spores begin to germinate, bacteria grow and produce a deadly toxin and excrete gasses.
The disease affects both skeletal muscle and cardiac (heart) muscle and is frequently found in both the leg and the heart. Of the skeletal muscles, the thigh (hindquarters) is most commonly affected.
If sheep or cattle have ever grazed the land you are currently pasturing, it is most likely you have the Clostridium chauvoei spores. This is why vaccination is so important for prevention.
Certain environmental conditions may cause the disease to become active in a pasture field. Fresh disturbances of the soil, such as tilling and erosion from heavy rains, can 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.
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.
Symptoms
Unfortunately, the most common first sign of blackleg is for producers to find a dead animal. This disease can kill within 12 hours of infection and usually does so in 48 hours. Contact your veterinarian immediately.
There are several signs and symptoms an infected animal will exhibit, including lameness, loss of appetite, depression, rapid breathing, fever and swelling. Sometimes the animal will appear lame on the affected leg before any other sign is noticed.
The swollen muscle starts out hot and painful, but it quickly becomes cold and insensitive as the muscle dies. Swelling with air pockets or gas under the skin is the classic telltale symptom of this disease.
Cl. chauvoei are anaerobic, which means they only multiply in the absence of oxygen. This bacterium attacks the muscular skeletal system of the animal. As the bacterium multiplies in the animal's muscle tissue, toxins, called toxin A, and gas are released, causing damage to the muscle and swelling as gas accumulates under the skin.
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. The gas, which builds up under the skin, makes a crackling or rattling sound known as crepitation when the skin is pushed down over the affected area.
Deceased animals need to be dealt with immediately. Pick animals 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 Clostridium 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 cannot reintroduce the carcass and its spores to your herd.
Importance of Vaccination
As previously stated, blackleg has an extremely high mortality rate, near 100%. Vaccination is needed for prevention, and many multivalent clostridial bacterin 7-way vaccines are available on the commercial market for livestock producers. Vaccines are very effective and inexpensive.
It is a very inexpensive insurance policy to protect animals with vaccination. Most blackleg products will cost producers approximately $1.20 to $1.60 per head, plus the cost of labor, depending on the product used.
Blackleg vaccines protect against several clostridial diseases, including Cl. Chauvoei (blackleg), Cl. Novyi (black disease), Cl. Septicum (malignant edema), Cl. Sordelli (gas gangrene), and Cl. perfringens types C and D (various types of enterotoxemia).
An 8-way vaccine contains an additional agent, Cl. Haemolyticum, which causes redwater disease in cattle, but it is not prevalent in West Virginia.
Clostridial vaccines are usually labeled as toxoids or bacterintoxoids, because the antibodies produced by the vaccine actually neutralize the deadly toxin produced by the growing bacteria, rather than the bacteria alone.
When using 7-way blackleg vaccines, they require a two-shot series administered three to four weeks apart. For example, for cattle, give the first vaccination at 60 to 90 days of age or when the calves are first processed. Then, administer a 7-way booster dose in four weeks or at weaning. Animals must be vaccinated annually.
One product, Alpha-7 (Boehringer Ingelheim), only requires one dose, but calves vaccinated under three months of age must be vaccinated again at weaning or at four to six months of age to be protected.
Many producers ask if adult cattle need a blackleg vaccine. Incidents of blackleg are rare in cattle over two years of age, but it can happen. Annual vaccination of adult cows will boost their immune response, plus they will produce antibodies in colostrum milk to provide stronger protection for calves.
Good quality colostrum from the dam will protect the calf from disease for up to three to four months of age until vaccination is effective. Work with your local veterinarian for recommendations and individual farm consultations as part of a good working veterinary client patient relationship.
ReferencesM.B. Irsik. “Blackleg in Cattle”. University of Florida Extension Fact Sheet VM165. March, 2007.
Michael Fisher. “Blackleg is Still Around?” High Plains Journal. Colorado State Extension Service. February 11, 2008.
Michelle Arnold. “Blackleg: Frequently Asked Questions.” University of Kentucky Veterinary Diagnostic Laboratory. Ohio Beef Cattle Letter. November, 2020.
Authors: J.J. Barrett, WVU Extension Agent – Wood County, and David Richmond, WVU Extension Agent – Raleigh and Summers Counties
Last Reviewed: March 2022
Trade or brand names used in this publication are for educational purposes only. The use of such product names does not imply endorsement by WVU Extension to the exclusion of other products that may be equally suitable.