I'm not a vet, but I know that what other drugs such as amoxicillin, chickens get almost the same dosage as a human being. These dosages are usually available from veterinary drug books. Dawg53 knows a lot more than I do about worming, but he hasn't been online in awhile. His later posts about worming are very reliable. When this sight started about 8 years ago worming was very different, but due to ivermectin and some drugs becoming ineffective due to resistance from the worms, the later posts are better to read.
Thanks. I have another thought regarding the effectiveness of Ivermectin on worms. Does resistance depend on whether you have used the product on your birds or premises before? I'm well out of city limits, we had a few cows eons ago and may have used the product once. Neighbor has had cows forever though. I've never used the product on my chickens though. So, if a person is in an area where the product has never been used or used slightly, would effectiveness still be reduced?