College of Veterinary Medicine

Veterinary Clinical Pharmacology Lab 

Affected Breeds


  Affected Breeds of Dog
Pictured from top: Collie, Australian
Shepherd and Silken Windhound.
Approximately three of every four Collies in the United States have the mutant MDR1 gene. The frequency is about the same in France and Australia, so it is likely that most Collies worldwide have the mutation. The MDR1 mutation has also been found in Shetland Sheepdogs (Shelties). Australian Shepherds, Old English Sheepdogs, English Shepherds, German Shepherds, Long-haired Whippets, Silken Windhounds, and a variety of mixed breed dogs.


The only way to know if an individual dog has the mutant MDR1 gene is to have the dog tested. As more dogs are tested, more breeds will probably be added to the list of affected breeds.

Breeds affected by the MDR1 mutation (frequency %)

Breed Approximate Frequency
Australian Shepherd 50%
Australian Shepherd, Mini 50%
Border Collie < 5%
Collie 70 %
English Shepherd 15 %
German Shepherd 10 %
Herding Breed Cross 10 %
Long-haired Whippet 65 %
McNab 30 %
Mixed Breed 5 %
Old English Sheepdog 5 %
Shetland Sheepdog 15 %
Silken Windhound 30 %
Last Edited: Dec 19, 2014 10:00 AM   

Veterinary Clinical Pharmacology Laboratory PO Box 609 , Washington State University, Pullman WA 99163-0609, 509-335-3745, Contact Us Safety Links