The link below is a table detailing the FDA approved anthelmintics. Not all of the anthelmintics listed are labeled for sheep. Check the FDA approved species column (4th from left) to make sure it is safe to use with sheep.
The parasites that infest sheep can be an enormous drag on sheep production. Year in and year out, they probably cause more death and disease in some producers’ lamb crops than any other single factor, including predators.
Powerpoint slides from a presentation by Dr. James Miller at the 2012 National Sheep Symposium
Collecting fecal samples for analysis is a dirty but necessary job. An analysis is used to identify and determine the number of parasite eggs present in an animal’s feces. Higher counts indicate a higher worm burden. The decision of whether or not to worm and what wormer to use is based on a fecal analysis.
Parasites are largely thought of as a limiting factor in sheep production, especially on pasture. According to the SID Sheep Production Handbook, larval development on pasture and the subsequent ingestion of the infective larval by sheep is affected by many factors, especially temperature and moisture.