HELP New Hens Have Lice!!

[Chickenkeepr]

I just purchased 9 replacement hens. I've only had chickens a couple of years and have never dealt with anything like this. The previous owner said that a couple of them were broody (they had bare bottoms) and me with no broody experience went along with it. I should have checked them there. Their bottoms are red, kind of dry looking, and bald. I did see a couple of lice roaming around right below the vent on 2 of them. I will be treating all birds including the 4 I already had. My question is..she gave me a can of Garden and Poultry dust. Is there an egg withdrawal period on this? I have read to dust their bottoms, as well as under their wings. Is there anything else I should know?

 

[Chickenkeepr]

I've also read about Ivermectin. Would it harm the hens that don't have lice? I have Ivermectin on hand for the horses and pot bellied pig as well, would either of those work? @casportpony any insight on this one? I can get pic later this afternoon. Also, should I put anything on their red bottoms to help soothe them?