Would this also work for internal worms? I have seen a few places mentioning putting the drops under each wing and on the vent area.. for internal and external parasites.. is there a withdrawal period for the eggs? And how often do I apply?I think you might have feather mites, which are not visible to the naked eye. Ivermectin pour on for cattle, a couple of drops on the back of their necks. Repeat in 10 to 14 days. The broken feathers will not improve, you will have to wait for then to molt naturally.