Australian Shepherds, along with several other mostly collie-type breeds, can carry a genetic mutation that makes them sensitive to certain drugs. Use of those drugs can cause serious neurological illness or death.
Fortunately, there is an extremely accurate DNA test that will let you know whether your dog has this mutation. All you have to do is provide a cheek swab. It isn't even necessary to go to the vet.
What is MDR1?
MDR1 is the abbreviated name of a gene called Multi-Drug Resistance 1. A mutation of this gene causes sensitivity to Ivermectin and a number of other drugs. Dogs with the mutation will react to those drugs. Having two copies of the mutation will lead to drug reactions, but having a single copy can also confer some sensitivity with some drugs. Dogs with this mutation have a transport defect - the drug goes in to their brains, fails to be transported out, and builds up to toxic levels. This causes serious neurological problems including seizures and sometimes death.
Which drugs cause reactions?
Ivermectin was the first drug recognized to cause a reaction, but it is far from the only one. Ivermectin at low dosage, as found in heartworm medications, will not cause a reaction. The larger doses needed for worming will. Other commonly administered drugs on the list include acepromazine and Imodium. Fortunately, there are alternative medications available if your dog requires treatment.
The drugs involved can be found on the website below.
This site offers a "medic alert" type collar tag for MDR1 dogs and has more extensive list, including alternate and generic names for the drugs:
Dogs that do not carry an MDR1 mutation may safely receive the listed drugs.
Which breeds are affected?
How common is the MDR1 mutation in Aussies?
32% of the Aussies and 49% of Mini-Aussies have at least one copy of the gene.
How do I know if my dog has the MDR1 mutation?
If your dog has already reacted to one of these drugs, it has the mutation. However, reactions can be so dangerous to your dog it is advisable to have the dog tested so you know whether it is sensitive before it receives any of the listed drugs.
What do the MDR1 test results mean?
This is a DNA mutation test. It will determine whether or not a dog has the MDR1 mutation and, if it does, whether it has one copy or two. The test report will provide you with the genotype for your dog, generally listed as Normal/Normal, Normal/Mutant or Mutant/Mutant.
Dogs with even one copy of the mutation should be considered sensitive to listed drugs. If your dog carries the mutation, provide a copy of the test results and a copy of the listed drugs to every veterinarian who treats your dog and let them know your dog cannot have those drugs.
What dogs should be tested and how often?
Since this is a DNA test, a dog only needs to be tested once. Due to the high frequency of the mutation in the breed and the variety of drugs to which dogs with the mutation can react, all dogs, including rescues of unknown parentage and Aussie-mixes should be tested. Their lives could depend on it.
The only exception is as follows: If both parents of a dog have tested Normal/Normal, they cannot pass on the gene and their offspring will not need to be tested. However, if a Normal/Normal dog is bred to one of unknown status or one that has even a single copy of the mutation, the offspring must be tested.
How do I get the test done?
For those in North America, The test is available through Washington State University. Information can be found on their website:
In the UK, the test is available through
In Europe the test is available through Genetic Counseling Services in the Netherlands:
In Australia, Genetic Technologies Ltd. and Gribbles Veterinary Pathology offer the test.
What does having MDR1 dogs mean to my breeding program?
You may breed dogs carrying the MDR1 mutation, even if they have two copies. MDR1 dogs react to certain drugs. Before these drugs were introduced into veterinary practice, no one was aware this mutation existed, even though it has been around for at least a century and a half. The MDR1 listed drugs, while valuable for veterinary care, are not a part of nature and can readily be avoided when you know a dog's MDR1 status.
Breeders should consider the mutation to be a fault, but not a disqualifying one. Dogs with the mutation would best be bred to those that are Normal/Normal. If this practice is followed consistently the frequency of the mutation will be reduced as time goes by and there will be far less risk of an untested dog succumbing to a reaction..
Test your breeding stock as per the recommendations above. You might want to consider testing all puppies that have at least one parent with the mutation. At the very least, provide your puppy buyers with copies of the parents' reports and urge those whose puppies may have inherited the mutation to get their dogs tested. Puppy buyers should be instructed to provide copies of the parents reports to their veterinarians so that their puppy will be treated appropriately as regards the listed drugs. If the puppy has been purchased for breeding, make the new owner aware that MDR1 testing should be considered as necessary as hip and eye exams and should be done before the dog is bred.
As time goes on and more dogs are screened, you could determine the need for screening any particular dog by checking the pedigree for known test results. If you find Normal/Normal ancestors along every line of descent, there's no need to test. But if even one line is unknown or has a dog with at least one copy of the mutation, you should test it.
The MDR1 test was recently added as an optional Canine Health Information Center (CHIC)
requirement for Aussies. Check OFA's website for
information on how to submit your test results. Dogs out of two Normal/Normal tested
parents that have been registered with OFA can receive a certificate with a CBP (cleared
by parentage) notation without having actually been tested themselves.
Does the MDR1 mutation cause epilepsy?
MDR1 drug reactions are not a form of epilepsy, nor are they in any way related to epilepsy, which is caused by different and as yet unidentified genes. The MDR1 mutation is one of the many things that can cause non-epileptic seizures. The drug reaction is very different from primary epilepsy. The dog will only seize if the chemicals build up in its brain. Treatment is different, prognosis is different and the seizures themselves may be different in presentation. MDR1-related seizures only occur if a susceptible dog is given one of the listed drugs. Once the drugs finally clear from the dog's system, the seizing will stop. If the dog does not receive those drugs, it will not have seizures due to the MDR1 gene.
Since the frequency of the MDR1 mutation is so high in Aussies and Mini Aussies, it is
possible that an epileptic dog could also have the MDR1 mutation. Such a dog would have
two diseases, not one. It may be possible that if an epileptic dog suffered an
MDR1-induced seizure episode, that might trigger subsequent epileptic seizures. MDR1
seizures will always closely follow administration of one of the listed drugs. Seizures
in epileptic dogs will have no relationship to whether the dog did or did not have those
drugs, unless the dog is both epileptic and MDR1.