I understand that there is reason to believe that Ivermectin doesn't work for lice, but I used it topically on my chickens in the evening and the lice were all gone the next morning.Read about poultry lice in this link if you need convincing that ivermectin wont treat lice.
http://ohioline.osu.edu/vme-fact/0018.html
More detail for you, "Chewing Lice," 4th paragraph, then read about all the different types of lice chickens get and what they feed on.
http://edis.ifas.ufl.edu/ig140