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MDR1 Mutation

While you may not be a scientist or savvy about the world of genes, as an owner (or potential owner) of an Australian Shepherd you need to be aware of MDR1.  MDR1 stands for 'Multi-Drug Resistance 1' and it relates to a mutation of this gene that can cause sensitivity to several drugs. Australian Shepherds commonly carry MDR1 mutations, but it certainly isn't limited to this breed. Collies, Long-Haired Whippets, Shetland Sheepdogs and German Shepherds are some of the other breeds which also can carry the mutation.  Fortunately there is a test which can determine if your dog is carrying one or two copies of the gene through a simple cheek swab that doesn't even require a vet visit.  The test results will determine if zero, one or two copies of the gene are present by identifying a Normal/Normal, Normal/Mutant or Mutant/Mutant result.  Even if your dog has only one copy of the gene, you should consider your Aussie to be sensitive to the listed drugs and never expose them. Knowing about your dog's genetics can save them from possible neurological illness or death if they were ever to come into contact with the list of drugs below:

  • Acepromazine - Tranquilizer
  • Butorphanol - Analgesic
  • Emodepside - Dewormer agent
  • Erythromycin - Antibiotic
  • Ivermectin - Antiparasitic agent
  • Loperamide - Antidiarrheal agent
  • Selamectin - Antiparasitic agent
  • Milbemycin - Antiparasitic agent
  • Moxidectin - Antiparasitic agent
  • Vincristine - Chemotherapy agent
  • Vinblastine - Chemotherapy agent
  • Doxorubicin - Chemotherapy agent

Testing for the MDR1 mutation can be performed through Washington State University.  

In September of 2015, our breed witnessed a very extreme case of ivermectin toxicity.  It happened in Massachusetts.


Laura Liebenow's 4-year old Australian Shepherd, Bristol (Ch. Maine-ly Hdstrong I'll Take U On) fought hard for her life after eating sheep poop at a herding lesson, not knowing the sheep had just been wormed with ivermectin. Her official diagnosis was ivermectin toxicity.  She suffered multiple seizures, and was immediately rushed to Tufts University where she was promptly put on a ventilator.  It took 10 days for Bristol to be able to breathe on her own, and three weeks for her to wake up from her coma.

The hospital performed a myriad of tests during this time period, from MRIs to bloodwork, and all showed healthy vitals.  Once Bristol awoke from her coma, she slowly was able to lift her head, and then made little bouts of progress with her walking cart, and then slowly began to bear weight on her paws.  It was amazing to watch.  This story has a happy ending because of the amazing care she received at Tufts, the fast reaction of her diligent owner and also because the aussie community rallied behind Laura and Bristol to raise the $50,000 which was required for her full recovery.  The education and lessons that have been learned from this example are worth far more than the monetary sum which was donated.


Logo design by Ximena Barrera of BluNova Collection

The lessons to take away from this experience are:

  • Bristol is MDR1 M/N.  However, ANY breed or MDR1 status would have had a reaction in this situation due to the amount of ivermectin which she ingested.  Had Bristol been MDR1 M/M she likely would not have survived;
  • It is possible for a dog to recover from ivermectin toxicity and lead a normal life.  Unfortunately, finances are often what stands in the way of an owner being able to help their pet.  Bristol and Laura were very lucky;
  • If you are going to have your aussie around working livestock, you need to be proactive and ASK the farmers if their herds have recently been wormed with ivermectin.  Don't let what happened to Laura, happen to you;
  • TEST your aussies so that you are aware of their MDR1 status;
  • Help to educate others about the dangers of MDR1 and the drugs which can cause a reaction;
  • Search #BristolStrong on Facebook to learn all about Bristol's story.