I don't use heart worm meds at all. Instead I get my dogs tested twice a year (Spring and Fall), and if they did contract heartworm, I'd treat them homeopathically for it with Paratox. I've never understood why bother treating the dogs with chemicals for a potential problem that will lower and possibly compromise their systems with a product that is not 100% effective anyway so they are still at risk. And then if they do contract it, their already compromised systems are asked to take on stronger meds (chemicals) and fight off the worm ontop of trying to take on fighting the chemicals.
As a natural rearer, I'm for natural preventatives rather than chemicals in or on the body. Starting with good food, lots of exercise, minimal/limiting vaccinations (which aren't 100% effective either) - basically by boosting their immune systems so they can fight off most anything they may contract and keeping them in top condition.
As for lowering the chance of contracting heartworm. Heartworm is passed on through mosquitoes, so the best thing to do is try to prevent the mosquitoes from biting. I use natural (homemade) sprays and soaps that help repel not only mosquitoes but ticks, fleas and flies, plant mosquito/bug hating plants like pennyroyal, spray oil of garlic around the yard and spraying the dogs' area more often then the rest of the yard with the oil of garlic. By testing twice a year, if one of the dogs were to contract heartworm, I'd catch it early and be able to deal with it easier and with less stress/damage to the dog's body and the worm will be easier to expel and do less damage to the heart as it wouldn't have had a chance to grow as much as it would if I only tested once a year or when the vet recommended to (I've seen vets give out meds without testing being done).
I have 3 labs....I feel your pain!
