I have to side with the no merle X merle crowd. There's something deeply repugnant about breeding a "perfect" dog at the cost of the lives of puppies. Perhaps in a very small breed it would be justified on rare occasion, but there is no shortage of good Aussies in the world. Its not the culling I find repugnant here . . . its creating a 25% chance per puppy of a need to cull that's really disturbing.