ivermectin for encysted strongyles?


My girls are due for their annual treatment for encysted strongyles. I was a bit surprised to see ivermectin recommend as a treatment, since I've only seen moxidectin or fenbendazole recommended. I see there's some concern about the fenbendazole causing ulceration to the colon, which is something I definitely want to avoid. But 2 of my horses are minis, so Quest isn't an option for them.

Where is the evidence that Ivermectin is actually effective in targeting encysted strongyles?

I've read through the 2013 deworming guidelines, but I didn't see any links to proof of ivermectin's efficacy for this purpose.

Bella received a dose of Quest in June. Does that mean she's covered for the year for encysted strongyles? Before Quest her FEC was 80 strongyles.  After Quest her FEC was 1 strongyle.




Lorna Cane

In Message 182434,Dr. Kellon says,"For encysted Strongyles, use either Quest or regular dose ivermectin for 3 treatments, three weeks apart. "

Lorna in Ontario,Canada
ECIR Moderator 2002
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Lavinia Fiscaletti

Hi Erin,

Ivermectin won't target the encysted strongyles directly. It kills the egg laying adults. Then some of the encysted strongyles, if there are any, will emerge to take their place. Dose again to eliminate this 2nd batch. Then do the cycle again to catch any stragglers.

FEC doesn't test for encysted strongyles. Are your three turned out together? If so, need to deworm all of them on the same schedule/time so they don't pass things off one to the other.

Lavinia, Dante, George Too and Peanut
Jan05, RI
EC Support Team

Eleanor Kellon, VMD

The ivermectin protocol is not published but I ran it past Dr. Gene Lyons (parasitologist in Kentucky) and he agreed it would work.

Eleanor in PA
EC Co-owner
Feb 2001


Thanks Dr Kellon. I just wanted to double check before I did anything, since I've never heard of doing this before.