It’s well known that buffalo, especially young or stressed individuals, are susceptible to internal parasites. This is exacerbated by the fact we now intensively graze large concentrations in smaller areas. Bison grazing in the wild or on huge tracts of land are constantly on the move, and so seldom re-expose themselves to parasitic larvae. But in small enclosures, the parasitic burdens can become huge very quickly. Controlling internal parasites must be an integral part of your herd-health program.
Have your veterinarian do various fecal samples throughout the year to determine how great the parasitic burden is in your herd. These are easy to do and almost always are done in house so results are quickly obtained. Keep in mind parasitic numbers are often falsely lower in the winter. Parasites are survivors so will reproduce more eggs in the warmer months and fecal counts at this time are a truer reading.
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Also, some species of worms produce fewer eggs than others. If using a quantitative test, any egg counts of 10 eggs per three grams or greater are considered significant. If you can observe individuals passing manure and can gather random samples of fresh manure from 10 per cent of the herd, it will give a good average of where the herd is. A few different species can be identified by their eggs and some are more significant than others. Your veterinarian can best advise how serious your problem is. If lungworms are suspected, a different type of fecal flotation is done (again usually in house) but the results take several hours to quantify. There are no dewormers officially approved for use in bison in Canada (only Ivomec in the U.S.) so all applications would require a veterinary prescription.
Worms can cause mortality if severe enough, but poorer weight gains in young calves and poor fertility in mature stock are often the first signs. Dull hair coats, slower shedding in the spring or increased susceptibility to other diseases, such as pneumonia, may be your first clue worms are present. The two best times to deworm are in the fall at processing and at pasture where overwintered larvae and eggs are picked up. Wet, cool weather in the spring favour survival of parasitic larvae and increased worm burdens.
Treatment
The endectocides and benzimidazoles are all fairly effective in treating the internal parasites common to bison. Most producers I work with prefer the injectable since dosage can be finer tuned especially if weighing them at the same time. The pour-ons must not be applied when bison are shedding their winter coat, as any product applied on these dead hair follicles will not be absorbed. Push the application gun down through the hair to ensure proper absorption. These products are commonly applied in the late fall at the yearly processing along with any other procedures commonly done to bison such as pregnancy diagnosis and vaccinations. When comparing injectables to the pour-ons, the efficacy seemed the same as long as they were applied properly.
The dilemma I run into as a veterinary consultant comes after doing fecals in the late spring. If worm counts are up how do we effectively deworm at this time of year? Running bison cows with calves through at this time of year is out of the question. But several fairly good options are available to us. A product called Safeguard (active ingredient fenbendazole) is very effective when administered in the feed, and many producers give their bison grain as a treat once in a while. Provided trough space was adequate, and all or most of the herd were consuming the grain at once, mixing Safeguard in could have desirable results. There are always a few timid animals that hold back, however. The other way is mixing the product in the minerals to be consumed over several days. All these applications will need a veterinary prescription, so talk to your herd veterinarian to help facilitate this.
There is no doubt internal worms are one of the main diseases which can severely affect bison and levels can build up over a few years where death can result, even for adults. Deworm your herd at least once a year by the methods indicated and this will go a long ways towards keeping your bison healthy.
These same principles can apply to cattle at pasture. Although they don’t generally have fatalities from worm burdens, production losses in the form of weight gains do occur. One day we can possibly look forward to a water-soluble dewormer that might be the easiest at treating bison at pasture. Resistance by worms to some of the dewormers is already happening in the cattle industry, so if in doubt check some manure samples to make sure the products you are using are working well. By keeping your bison as worm free as possible, weight gains will be higher, reproductive rates better and disease incidence will be lower as parasites tax the immune system.
