I'm wondering what you are going to use Ivomec for now?
Where we live we are definitely 'off season' for it. Too late for fall worming and wayyyyyyyy too early for strategic worming in spring. That wouldn't be til mid-June, first of July. If we don't get some moisture, we sure won't need to de-worm anything as it takes moisture and temperature for worms to be active.
Interesting the price on the Avermectin products came down about the same time as it lost effectiveness. Cattle are starting to show an immunity to it~running fecals after using it, often shows only 50% kill.
BTW, it has been our experience that Cydectin is the worst of the lot.