We have an Australian Shepard and nearly lost him after using it. We found out that the breed has a mutation MDR1. And is not recommended. We were terrified and have went to a topical called Revolution. Sorry the product we had a bad experience with was Heart guard which is not a topical........ My bad.
I believe that its not recommended for any collies or sheppards. Ive used it on hounds, beagles, labs, feist, setters and pointers to great success and savings. I believe in it. I have a great deal of money in my dogs and I dont play around with there health but ivomec is the pure source for heartworm prevention.