Resistance to dewormers is extensive and officially includes almost all deworming drugs except ivermectin and moxidectin. However, with isolated reports of possible ivermectin resistance beginning to appear in horses, as they have in cattle for many years, we're skeptical about no ivermectin resistance.
To learn more about deworming your horse, download a FREE guide—Deworming Your Horse: How to find the best deworming schedule for you and your horse.
For resistance to develop, the parasite must be exposed to the drug one or more times. For this reason, many experts now advise that healthy adults should not be dewormed on a regular schedule of every X number of weeks.
Simply rotating deworming drugs on schedule doesn't stop resistance from building. You have to break away from the calendar-based rotation deworming schedules. By doing so, you'll avoid unnecessarily exposing the parasites to the dewormers, which would increase the likelihood of resistance.
Where's That Deworming Rotation Drug Schedule And Calendar?
We know most magazine articles give you a standard deworming schedule to use on your horse all year long. We used to do that for you, too. We even broke it down by type of horse. Obviously, it's easier to mark the deworming type that's due when on your calendar, as in "May: deworm with double-dose pyrantel pamoate; July: deworm with strongid" and so on. However, you may be wasting money with this type of schedule. Many horses don't need the manufacturer-recommended heavy deworming rotation. Start by deciding what your horse needs.
