We've been using VERM-X for sheep and poultry. I've just ahd a faecal worm egg count back for the sheep and it was <50 ie they coudl see no eggs in the faeces at all. This doesn't mean they don't have worms but the levels are low. To be fair, they were wormed traditionally before I got them and they went on to grass that had only been grazed by sheep escaping from the field next door for years, so the grass was pretty clean. I don't intend to worm again but will have regular counts done.