Friday, October 23, 2015

Veterinary Highlights: The Need for Genetic Testing in Herding Breeds

Just recently a 4-year-old Australian Shepherd almost died to ivermectin toxicity.

She required aggressive care, including breathing ventilator. It took 10 days before she started breathing on her own again and she remained unconscious for three weeks. No earlier than after a month of treatment she was herself again and could eat, drink and walk on her own.

Not many cases of ivermectin toxicity in white-footed herding breed dogs have happy endings.

Do you have a herding breed dog? Did you get the multidrug resistance (MDR1) test done?

Many herding breed dogs have a genetic predisposition to adverse drug reactions involving over a dozen different drugs. The most serious adverse drug reactions involve several antiparasitic agents (ivermectin, milbemycin and related drugs), the antidiarrheal agent loperamide (Imodium), and several anticancer drugs (vincristine, doxorubicin, others).

These drug sensitivities result from a mutation in the multidrug resistance gene (MDR1 gene).

About three out of every four Collies in US have the mutant MDR1 gene.

Affected breeds include Australian Shepherds, Border Collies, Collies, English Shepherds, German Shepherds, Herding-Breed-Crosses, Long-haired Whippets, McNabs, Old-English Sheepdog, Shetland Sheepdogs and Silken Windhounds.

Affected gos can suffer suffer life-threatening illnesses or even die if given certain parasite-control products, antibiotics, sedatives, chemotherapy drugs and pain medications.

Source article:
After Dog's Recovery, Tufts University Reminds Owners About the Need for Genetic Testing

Further reading:
What is MDR1?
Multi-Drug Resistance Gene (MDR1)
MDR1 Mutation Affected Breeds
Multidrug Sensitivity: What You Need to Know


  1. This was a concern when we brought Scout and Zoey home and our vet made a note in their files that they're Aussie mix and will test them should we need to do any major procedures. It was a relief that my vet understood and shared my concern.

    1. It's always great when the vet appreciates the concern. It's always better to be safe than sorry, particularly with such things.