Closely follow a drenching program for all sheep grazing on irrigated pastures. Often, treatment is too late if it is delayed until a diagnosis is made. In general, moist conditions and temperature should influence the time of drenching. Seasonal treatments should be designed to reduce worm burdens at critical periods. Treatment at these times should have two objectives: first, to prevent the build-up of heavy infections in the animal, and second, to reduce contamination of pastures with worm eggs. Drenching ewes before they are put on pasture, during the summer as needed when they are rotated to fresh pasture, and in the fall before they are placed in a drylot or on field cleanup, could fit into many management plans.
A drenching program can be adapted to the production system. Drenching lambs at weaning is beneficial in preventing a build-up of parasites. Lambs are much more susceptible to parasitism, although lambs that are born early and marketed without going to pasture usually do not need to be drenched. Throughout the year, alternate between at least two different drenches. If only one product is used, parasites that are not eliminated can become at least partly resistant to that particular drench. Common drenching products include phenothiazine, thiabendazole, Tramisol, Loxon, and Ivermectin. Sheep may have free access to phenothiazine salt mixture during the pasture season, but this should not replace a regularly scheduled drenching program.