The drug sensitivities you are concerned about are genetic in nature, and are not guaranteed to occur in all collie or sheltie puppies.

IF your dog picks up mange, then it would probably still be possible to try invermectin at 1/10th it's normal dosage and gradually titrate up. Your Vet might have an idea as to where to start.

In remembering back to when my Barney had his demodex mange, the first two doses were sub-doses to see how well he tolerated the invermectin. Which is probably a wise way to give such medication to any breed of dog.

P.S. Barney is part black lab, and who knows what else.