photo 2009 Daisyree Bakker | more info (via: Wylio)
I have two Shelties and the two vets in the office where we go have different opinions on Heartgard for Collie type dogs. One perscribes it and the other says not to use it. What is your opinion?
My opinion, and more importantly the opinion of numerous veterinary toxicology gurus, is that Heartgard Plus is safe for Collies and Shelties.
Heartgard (it always pains me to type that word — I wish the manufacturer had decided to spell guard correctly) Plus is used in dogs as a monthly heartworm and intestinal worm preventative. It contains two active ingredients. Ivermectin prevents heartworm infestation by killing larvae in the bloodstream. Pyrantel pamoate removes many types of intestinal worms.
Collies (including Border Collies, Bearded Collies, and Rough Coated Collies), Shelties, and dogs with pigmented bodies but white feet are prone to a genetic anomaly called the MDR-1 mutation. Dogs with the mutation are susceptible to toxicity from a number of medications. Ivermectin is the most famous and widely used of the medications that can cause toxicity in many Collies and Shelties.
This fact has led many vets to be wary of using Heartgard Plus in Collies and Shelties. However, the dose of ivermectin in Heartgard Plus (6 ug/kg) is only about 1/8 of the dose (50 ug/kg at least) that causes toxicity in individuals with the mutation. The consensus among experts therefore is that Heartgard Plus is safe for all dogs.
Ivermectin commonly is used at higher doses to treat various types of mange and other parasitic diseases. High-dose ivermectin is a huge no-no in Collies and Shelties unless they are first tested for the mutation.
The test for the mutation is readily available through commercial veterinary diagnostic laboratories. I recommend it before starting a course of high dose ivermectin in any dog. However, I do not worry about toxicity when I prescribe Heargard Plus.