Well as a former barn manager..Listen up clients.. it may be YOUR horse and YOUR fee..but it isnt YOUR barn and there are other clients there also.Most contracts state to some effect that you must maintain your horse to the standards and practices set by the barn. If you fail to do this, Barn Manager may tell you to go find another place to board.
In a case like this the barn manager has every right to require doing this as tapes are transmittable.(unlike if say a potomac outbreak happens and they advise you to booster).Especially if it comes with a vet recommendation..now any vet /barn manager should also be flexible enough(or maybe I should say informed enough) in THIS case to see that the pyrantel chemical will do the same job as the other chemical.My vet always advised us to double dose strongid until the new dewormers came out..then she said it was up to my discretion.