The Smooth Collie is a breed of dog developed originally for herding. It is a short-coated version of the Rough Collie of Lassie fame. Some breed organisations consider the smooth-coat and rough-coat dogs to be variations of the same breed. Multidrug sensitivity (MDR1): Sometimes fatal reactions to a class of common drugs, particularly ivermectin, used as a heartworm preventative and treatment for mites. The gene that causes this sensitivity has recently been identified, and a dog's susceptibility can now be determined through a simple blood test.