Did you know that 1 in 4 Collies could have a mutated MDR-1 gene? Aussie and Mini Aussies are susceptible too.
Recently a few different studies have identified that dogs with a mutation in the MDR-1 gene are more susceptible to having allergic reactions to certain chemical classifications. Dogs with this sensitivity can suffer acute and often fatal neurotoxicosis (poison of the nerve tissue in the brain or spinal cord.)
The primary concern is with ivermectin sensitivity. Ivermectin is the primary ingredient in Heartgard heartworm prevention, but is also the drug used to treat dogs that are diagnosed as heartworm positive.
While even dogs with the sensitivity SHOULD be able to tolerate a dosage suitable for heartworm prevention, if you have a dog that ranks higher on the susceptibility list, you may want to consult with your veterinarian.
Breeds affected by the MDR1 mutation and approximate frequency %:
Collie 70 %
Australian Shepherd 50%
Australian Shepherd, Mini 50%
Shetland Sheepdog 15 %
German Shepherd 10 %
Old English Sheepdog 5 %
Border Collie < 5%
A complete list of breeds can be found in the report from Washington State University:
For more information on ivermectin sensitivity visit the American Working Collie Association drug sensitivity page: http://www.awca.net/drug.htm.