I know going to the vet is the best way but really can't afford it right now. A co-worker told me they use horse wormer (ivermectin) for their dogs in stead of the vet's office heartworm pills because it is cheaper. Has anyone else done this? Which one is the best to use? I have talked to a few people and have been told two different types, the liquid and the paste. It would be for a large Newfoundland/Lab-mix 120lbs.