Here we have to worm every two months, just like we do with the horses. As we cannot rotate pastures.
We also use Safeguard and Panacur for the lambs.
Ivomec (have used with ewes in lamb with no problems), and rotate with Dectomax for the adults not in lamb. The only caution with Dectomax is you "have" to know your sheeps weight, not just guess.
We have found Valbazen really doesn't do any thing for us. There are alot of places in the country, that it no longer works well.
So far I have no had a Liver Fluke problem, as I run ducks in the pastures and that is one of the creatures Ducks live to eat.
The lambs also get a Coccidial Prevention feed starting when they are 1 month old.