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.
A link to a British educational review of on sheep de-worming issues and practices. It includes information on peak infection times, when and when not to de-worm and how it should be done. We’ve included it because it makes a complicated subject unusually easy to read and understand.
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.