As a veterinarian, I may have a different perspective, but regardless of what you are using as a dewormer there is naturally some parasitic resistance to the drug. Just like with antibiotics, there is no silver bullet medication that takes care of them all. So...the longer a medication is used, be it a dewormer or an antibiotic, the more likely a resistance to that medication will arise. There are different dewormers manufactured because of this fact. So... if you want to ensure that you are keeping the parasitic burden as low as you possibly can in your horses then rotating dewormers is the best way to achieve that. Lance Campbell, DVM Bay Equine Veterinary Practice www.bayequinevet.org
