Absolutely believe in zapping and have not used the ivermectin. Bought it in case. Not just for the dog, but just in case my chickens come down with a bad case of strongyloides. Ever try to zap a couple dozen hens and a rooster. Those old roosters get mean when you start messing with their harem. Of course, if you give them ivermectin, you can not eat the eggs for a couple of months.