Animal health matters: Grazing cattle on short pastures can increase anthrax risk

Russ Daly
South Dakota State University Extension

Of all the cattle diseases producers need to worry about, anthrax is one that usually registers quite a bit of concern when reports surface.

While conditions such as bovine respiratory disease or calf scours are more consistent and economically important to beef operations year after year, the term “anthrax” grabs attention from non-producers and producers alike.

For most of the public, anthrax evokes thoughts of biological weapons and terrorism. For those defending our country, this threat remains a concern. Cattle producers, however, know it as a potential cause of death for cows and bulls on pasture.    

In cattle, anthrax is caused by a bacteria that survives for years — even decades — as a very tough spore form in the soil. When cattle graze short pastures or when these spores have been washed up on grass from previous pasture flooding or dug up during excavation, they’re more available to be eaten by the cow or bull.  

Once the spores have been eaten by the cow, they move through the gut wall and multiply rapidly in local lymph nodes, eventually becoming distributed throughout the body. As they proliferate, the bacteria produce toxins that cause shock and rapid death — so rapid, that usually the only sign of disease is simply cattle found dead in the pasture. One interesting feature of anthrax in cattle is that blood doesn’t seem to clot after death; seepage out of the nose or other orifices is frequently reported. 

Certain soil types and climatic conditions favor the viability of anthrax spores in our pastures, but apparently the spores are quite widespread across the region. This fact is borne out by the observation that most areas of South Dakota have played host to anthrax mortalities at some time in history. Therefore, although we sometimes associate anthrax with the central part of the state, it can really pop up anywhere. An important risk factor this year is the widespread drought, increasing the chances that cows or bulls will graze close to the ground and pick up spores in the soil. 

Anthrax vaccine is highly effective at preventing death losses due to the disease. Those producers who haven’t used it this year should be vigilant about death losses on pasture. When unexplained death losses of cows or bulls occur on pasture, the carcass should be left undisturbed until a veterinarian can take an appropriate sample (usually a sample of blood from the dead animal). An animal that has died from anthrax can be a substantial source for new spores in the environment if the carcass is opened up or moved. 

If proper specimens are submitted to the lab, the diagnosis (or rule-out) of anthrax is fairly quick. The blood is smeared onto a microscope slide and stained with a special stain. If anthrax bacteria are present, they’ll absorb the stain, revealing a characteristic “line of train boxcars” appearance under the microscope. This quick screening test can provide a preliminary answer for the veterinarians while the bacteria grows in culture overnight (which is the confirmatory test). Of course, all this is done under strict lab safety procedures.

If the lab confirms anthrax as the cause of death, the diagnosis is reported to the state veterinarian’s office. Their staff works closely with the herd owner and veterinarian to make sure the surviving cattle are properly protected, and that any death losses are properly burned and buried. 

Another consideration with anthrax is the potential for it to cause infections in the people working with the carcasses. While not common, people can contract nasty skin infections if the bacteria enter through a cut or a scrape. This means that personal protection through gloves, coveralls and boots, along with proper disinfection of the equipment used in disposing of the carcasses, is extremely important to ensure people are not affected. The state health department will often send notices to local health care providers so they’re aware that cattle anthrax has been identified in the area. 

Anthrax is one of the more important reasons that sudden, unexplained death losses in cows or bulls on summer pasture should be investigated by your veterinarian. If anthrax is diagnosed, prompt vaccination and treatment of the remaining herd can greatly help limit further losses.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University.  He can be reached via e-mail at russell.daly@sdstate.eduor at 605-688-5171.