I try to post this every year near the anniversary of our dog's near death experience due to ingestion of Ivermection from tiny sliver of apple that must have had a slight film of ivermectin on it after I dewormed my horses and one of them dropped a piece of their post-deworming treat out of its mouth. Our part-bred collie, Burns, picked it up from the floor of the barn and ate it. I didn't think anything of it until hours later when he began falling down and acting completely out of it. I had no idea collies were so incredibly sensitive to ivermectin toxicity.
I took him right to the vet and I even brought the Zimecterin box to show him, but the vet diagnosed him as having hip dysplasia and gave him a sedative which almost killed him. By the time I got him home, I was absolutely sure it had to be poisoning because he lost bladder control and was completely ataxic. I called the vet and he returned my call minutes later, telling me to bring Burns back immediately. He had done some quick research and discovered that Ivermectin is toxic to collies and dogs that have collie blood in them. He admitted that he had never seen it or heard of it before, but thank goodness he was willing to finally listen to me or I'm sure Burns would have died.
So if you have a collie or a collie mix, be very careful when doing spring deworming with Ivermectin.
I thought it was toxic to all dogs, not just those with collie blood? Are collies more sensitive to it?
At high doses ivermectin is toxic.
At low doses, it is used as a heartworm preventive. It's the active ingredient in HeartGuard.
Some dogs have a mutation on the mdr1 gene that allows ivermectin to cross the blood/brain barrier. Here's a link to an article on which breeds seem to be most affected by the mutation. Scroll down for a chart of those breeds. Sounds like the OP's dog has that mutation.
But even dogs without the mutation can be poisoned by ivermectin, if they are treated with ivermectin and then exposed to another source, like the manure of livestock wormed with ivermectin.
Breeds affected by the MDR1 mutation (frequency %)
Breed Approximate Frequency
Australian Shepherd 50%
Australian Shepherd, Mini 50%
Border Collie < 5%
Collie 70 %
English Shepherd 15 %
German Shepherd 10 %
Herding Breed Cross 10 %
Long-haired Whippet 65 %
McNab 30 %
Mixed Breed 5 %
Old English Sheepdog 5 %
Shetland Sheepdog 15 %
Silken Windhound 30 %
70% of rough [Lassie collies] were affected. Pretty large percentage.
AFAIK, there's not been a documented case of a purebred border collie with the gene mutation. The "less than 5 per cent" comes from a shelter dog or two presumed to be border collies but of unknown parentage.
Have a friend who almost lost a wonderful Aussie this way! Please be careful with dogs in the barn at worming time. This dog just picked up a few grains that the horse dropped when eating after worming.
"One person's cowboy is another person's blooming idiot" -- katarine
We tested ours for the mutation (she didn't have it) and kept her away from the barn for 10 days after worming with ivermectin and Quest. We did manage to teach her not to eat manure, but it took a very long time. We use Interceptor.
For anyone who does have collie what do you give for Heartworm?
(one of ours is a smooth collie - we're not taking chances)
If I were you, I'd talk to a vet who is well-educated on the subject.
I wanted to post to be sure that everyone realizes that all macrocylic lactones are potentially fatal at high doses in dogs with the mutation. These drugs include, for example, milbemycin oxime (Sentinel and Interceptor). In addition, Interceptor will cause a mass microfilarial die-off in a HW positive dog which can lead to anaphylactic shock and death.
I know this because I nearly lost a rescue dog this way after a well-meaning vet used Interceptor as a microfilaricide after immiticide treatment. So please be sure the vet you consult knows what s/he's talking about - the vet who did this didn't realize that border collies have not been shown to have the mutation and so actually used a drug that was far more dangerous to my dog than ivermectin would have been.
OTOH, the research I've read suggests that at prophylactic doses, avermectins can be given to dogs with the mutation without ill effect.
There is also research looking into whether even those heterozygous for the mutation may have sensitivity, albeit much less severe than the homozygous mutants.
My MDR1 mutant dog (she is homozygous for the mutation), a border collie/aussie cross we think, gets Interceptor as her monthly preventative. She also gets tested yearly and I don't miss a month of preventative, so if in doubt probably test for HW before giving something like that to anything that might have the mutation (my vet also would test anyway prior to giving a dog of unknown origin b/c I think that reaction can occur in non-mutants as well if HW positive and given any of the meds).
I know they say that ivermectin is safe in prophylactic doses, but from what I have read the mutants still seem more sensitive to the avermectins than other antiparasitics used for HW so my opinion is why risk it?
I think that reaction can occur in non-mutants as well if HW positive and given any of the meds.
Not ivermectin, if given at the prophylactic dosage. In fact, that's how many of us here in HW areas treat HW+ positive dogs. You kill the microfilariae and the adults die of their own accord within a couple of years. It's called the "slow kill" method. Rescues use it a lot, as a way of stretching resources - but my last dog and cat vet actually recommended to all his patients as he believed it was safer for the dog than immiticide.