I have run across several clostridial (blackleg) outbreaks in bison over the years.
I will use the term blackleg to refer to most of the clostridial diseases bison get, even though only one specific one causes the true blackleg.
It is a spore-producing bacterium and the spores remain infective in the soil for more than 50 years.
Most clostridial diseases have similar clinical signs, which are severe depression, high fevers and lameness if the true blackleg has affected the muscles in the leg.
Most bison producers will find an animal dead. Death is rapid, often within 24 hours of the animal showing clinical signs.
Animals can survive another clostridial disease called redwater, because of red-coloured urine, for a few days.
All clostridial diseases are fatal and contrary to popular belief that mature bison cannot get blackleg, they can.
Producers should have autopsies carried out on any bison deaths and especially sudden deaths. The post-mortems must be conducted quickly because bison autolyze (break down) fast, which could make it difficult to determine cause of death.
While there are fewer bison deaths than cattle deaths caused by clostridial diseases, mature bison do get sick and die from it. That is a shame considering the vaccination has proven over the years to be very protective, achieving close to 95 to 100 percent effectiveness.
You will be using the cattle vaccine at the same dose for your bison. This is considered using it extra label in Canada and I believe it is used under the minor species status in the United States. It is best to check with your herd veterinarian and the specific vaccine they recommend for your area.
I tend to use as broad a spectrum vaccine as I can because there is always the possibility of some of the other clostridial diseases, such as tetanus, septicum and hemolyticum (redwater). Covexin plus or Tasvax are two commonly used ones but there are others.
When cows are vaccinated, they pass this protection to calves in their colostrum.
The vaccines are generally seven-way to nine-way vaccines, meaning they protect against seven to nine different clostridial organisms.
All vaccines are given subcutaneously in the neck so they must be given when processing bison.
If you use a short needle and come in at an angle, you will be subcutaneous, meaning under the skin. As well, use good access panels provided by most the bison chutes. I prefer to use the one-handed subcutaneous technique that does not involve tenting the skin. With bison sometimes jumping up and down even with head restraints, you are far less likely to get your fingers pinched with the one-handed method.
While it is not really possible in the bison industry to vaccinate young calves, there must be good colostral immunity transfer from mothers to calves because I have not seen a case in young bison calves.
One problem in identifying this disease in bison is that sudden deaths are often not discovered in time to conduct an autopsy because bison run in extensive ranges. It may be your only option to vaccinate calves at weaning and the cows whenever possible.
The vaccine-provided immunity from clostridial diseases may last several years (in humans we get a tetanus shot every 10 years) so my recommendation is once an animal has been administered two vaccines, vaccinate the cows whenever you get a chance and are catching and handling them.
The odds of picking up the clostridial organisms increase if soil disturbances have occurred, such as in areas where ditching or excavating have occurred. Areas where bison dust themselves are another source of infection. In dry years, swampier areas may be pastured, which may give bison access to exposed spores.
The transmission is similar to what happens with anthrax. Also similar to anthrax is these spores may remain dormant in the soil for decades. Anytime there is bruising, such as what happens with processing, sorting and vaccinating, increases the odds of the clostridial diseases as well.
As with any handling of vaccine, keep it from overheating and definitely not freeze it (maintain at refrigeration temperature as long as possible). Since most weaning happens in late fall or winter, keep an insulated warm pack if the day is cold. Freezing destroys the vaccine and renders it ineffective.
Administer to bison the amount recommended for cattle because there are no vaccines available that have bison on the label but check with your herd veterinarian. If you think you have not given the full dose, repeat it. Best to give it subcutaneous like all the other vaccines you may give to bison to eliminate any muscle damage, which shows up later in the meat.
Feedlots may use other vaccines to try and prevent respiratory disease but consult with your veterinarian to see which are recommended for your operation.
The clostridial diseases should be given on every beef, bison or elk ranch. Certain areas definitely have a higher incidence than others.
With cattle, the standard slaughter withdrawal is 21 days and we should maintain a longer time period than this in bison to be safe.
If purchasing new breeding stock with an unknown history, be safe and vaccinate because the vaccine is inexpensive and readily available, and immunity is very good. Administer booster shots of the vaccine when possible and continue to do it when bison are processed in the late fall or winter. The vaccine is safe on pregnant animals.
Bison are generally only vaccinated for a few diseases but clostridial disease is one of them.
Roy Lewis works as a technical services veterinarian part time with Merck Animal Health in Alberta.