MDR1 – Herding breeds may have a potentially deadly gene defect


This article does NOT contain affiliate links. Links are purely informational. I have tried to summarize the gene defect, but if you can’t follow along with my explanation, please visit the links for more information.


Genetic Defect in Herding Breeds


Correction 1/10/20:  My original post had incorrectly listed this gene defect as MRD1 – when it is clearly MDR1 – Multi-drug Resistance 1.  I corrected all the references to MRD1.  

Dogs in the herding breed category, which includes Collies, Australian Shepherds, and Long-haired Whippets may carry a mutated gene that inhibits their ability to process certain drugs. The mutated gene or gene defect also called Multi-Drug Resistance or MDR1 causes neurological issues, seizures or even death if the drugs are given in normal dosages.


Research & Discovery of the gene defect

Washington State University discovered the MDR1 gene mutation.  They also continue with research to update the list of affected drugs and affected breeds.  Washington State University currently holds the patent for the diagnostic test to determine if the gene is normal or mutated.  They also promote their officially licensed partner, Wisdom Health.  Wisdom Health includes the MDR1 test with their DNA test to analyze what specific breeds are present in a particular dog.

What is the Problem with the Gene?

Dogs without the mutation produce a normally functioning protein called a p-glycoprotein. This protein acts as a pump keeping chemicals and toxins from building up in a particular cell. In dogs with the mutated gene, the pump is abnormal and cannot drive the drugs out of cells. When the drug builds up in the brain without an available exit route, high levels of reach toxic amounts and cause neurological issues, seizures or even death.  Death depends on the dosage of the drug administered and the degree to which the dog has the mutated gene.

Does my dog have this mutation?

Herding breeds are the class of dogs that seem to have the greatest percentage of MDR1.  Collie, Australian Shepherd, and Long-haired Whippets have the highest occurrences. Mixed breeds are also at risk, so do not think this is strictly a ‘pure-bred’ problem.  The gene defect occurs in mixed breeds at a much lower occurrence rate of only 5%.  While mixed breeds with a known herding dog lineage boost the occurrence up to 10%.  And while 5% is a very low rate, if your dog possesses the gene defect, wouldn’t you want to know before it becomes an issue.  If your dog has some ancestors in some of the top herding breeds on this list, I suggest you have your dog tested.  It’s always better to be safe than sorry.

Chart showing occurance of MDR1 to specific breeds


How can my pup be tested?

Normal methods of testing are either a check swap or a blood test.  A vet can easily take a sample of your dog’s blood to send off for testing. I personally purchased the cheek swab test directly from the Washington State University website.  Cost is $60 per dog and you must pay online via credit card.

My dogs allow me to put my hands in their mouth and I can touch their teeth and gums.  Normally, I can even take a bone that they are chewing right out of their mouths. If you can do all this with your dog, I recommend the cheek-swab. If you think this will be difficult, I recommend having your vet draw blood.

What can you expect as a result?

Three possible outcome results come directly to your email.

Normal/Normal – No mutation of the gene.

Normal/Mutant – Your dog is a carrier of MDR1 and may experience some sensitivities to specific drugs. Offspring of this pup may be Normal/Normal, Normal/Mutant or Mutant/Mutant depending on the gene from the other parent.

Mutant/Mutant – Your dog is sensitive to specific drugs. Inform your vet and speak to him/her about alternative drugs.

What drugs to avoid if the test comes back as Mutant/Mutant

If your test result comes back as Mutant/Mutant or even if your dog is Normal/Mutant, you need to be aware of the drugs to avoid. This link provides the best up-to-date info on drugs that affect your pup if testing positive for the MDR1 gene.

If your dog possesses the defective gene, I suggest purchasing a collar or tag that designates the presence of the MDR1 gene. A tag will help identify your dog as having a drug resistance problem. A lost or hurt dog taken to a vet, for injuries, may administer one of the suspect drugs before an owner can be located. I would feel terrible if I found a hurt dog and my ‘help’ in taking them for medical assistance caused the pup, neurological issues.

If your dog has the MDR1 mutated gene, make sure that your dog stays clear of farms and/or farm animals.  Large animals are normally dewormed per herd, not by individual cattle.  The dewormer used is some form of Ivermectin, Selamectin, milbemycin, or moxidectin.  These types of medicines are used in preventative heart-worm medication for dogs but are also used for deworming large animals.  The small dosages present in heart-worm preventatives are even supposedly safe in Normal/Mutant and Mutant/Mutant MDR1 dogs.  However, if your normal dog visits a farm and steps in cow manure or horse dung, they can be ingesting toxic levels of these drugs as the cow or horse is much larger than your dog.  If your MDR1 dog ingests these same amounts, they may not be able to recover from such toxic levels.

Emergency Hospital Warnings

Also, when taking your MDR1 dog to a veterinarian and especially an emergency animal hospital, make sure that you announce their MDR1 status prior to letting anyone work on your dog.  If you give your consent at an emergency hospital, you are allowing the doctors to access and treat your dog prior to speaking to you.  Make sure you have a list of the drugs that need to be avoided or given in reduced amounts.

Apomorphine is a drug used to induce vomiting in dogs.  This could be used at an emergency hospital when a dog has eaten chocolate, or aspirin, or grapes or any of the many things that are toxic to dogs.  Make your dog’s status be known, even if you are a pain in the ass about it.

Veterinarians should consult with you before administering most of the other drugs on the list.


I read about this condition as I studied for one of my Vet Tech classes.  Statistically, 1 in 2 Australian Shepherds carry the defective gene.  I own two Australian Shepherds, so I knew immediately, that I would get my pups tested eventually, if only for my peace of mind.  MDR1 testing is suggested for any mixed breed.  However, when a herding breed is suspected in the linage, it should be an automatic test.  Has anyone seen this condition first hand?


Updated PIN for MDR1 article

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1 Response

  1. Jackie says:

    Help ? I adopted a young white border collie x , he needed broken teeth pulled and after was given trazadone which did not sedate him made him aggressive , fireworks are nearing time ? What can I give him as he does have the mdr1 status a so had him tested , tried cbd calming chews , um slowed him down a bit but I would love something more like safe sedation , my neighbors all go crazy with fireworks and I use trazadone on my other dogs , but not this one ? Any suggestions ?

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