I just purchased my Border Collie pup (8 wks. old) yeserday. I lost my 17 year old Border Collie last year. I was wondering if anyone was using Ivermectin based heartworm protection? (such as Heartguard). 17 years ago there was some problem with Collies using it. My Vet states that it is such a low dose there should be no problem. I was just wanting to know if anyone is using it safely. Thank-you..