I too have questioned using moxidectin (Quest) and actually had a vet out the other day for some other critters and I asked about it.
Specifically about using it in rotation with the others as per the AVMA recommendations and he said yes he recommends it. I asked about the problems associated with it and he said yes there have been some problems, but the issue is usually weight and not calculating it correctly. (Of note, this was more of a crusty old timer type of vet who was able to make a farm call. There are very few vets who make farm calls here and I usually have to load up and haul said animal to a good vet. But I can’t always do that.)
However, it is a known fact that some dewormers cannot be used in certain breeds of dogs but are fine for other breeds, so I am not surprised that some horses may react to moxidectin, even when used correctly.
Also, sometimes bad reactions in animals or people to a given medication or injection can be traced to the carrying agent than the actual drug is put into, and not the medication itself.
I also know that other classes or dewormers have much lower incidences of causing problems or they have a wider margin of error for many types of animals (in general.)
Because of all of this, I consider using moxidectin a calculated risk and since at this point there are other drugs to choose from within that rotation group, I personally choose not to use Quest even with one local vet‘s opinion that it is ok.
Last edited by Lockwood; 12-07-2012 at 02:46 PM.