Found it to be really good. My dad was recommended it years ago by our local feed stockist and we've used it most seasons since. Most I've used it is twice in one year.Usually 4-6weeks before pairing and occasionally used it during racing,usually in the 2nd last week in May.Personally notice a big difference in the birds after it.Never had droppings tested,before or after treatment.So can't really comment on just how effective it is on internal parasites but you'll not have any lice or crawlies on your birds for a long time after the dosage.