I have two silver laced orpingtons - Margaret and Mrs Warboys - and the poor girls have a HORRID infestation of lice around their vents and backside area. They're only about ten months old (and still haven't started laying!) but I've had these constant infestations since I got them home. My other chickens have never had lice and are fine with a dusting of powder every now and then (a little in their dust bath too) But the poor orps seem to battle it off and then succumb again!!! Today I had to cut a lot of their feathers to free up their backsides and SUDDENLY LICE EVERYWHERE!!! I check them every two weeks, so this is a very sudden onset. HELP!!! Has anyone tried Harka-mectin? My local feed store said they're not legally allowed to recommend it but they said this whilst theatrically nodding their heads in response to my question of whether or not it would help clear the lice. My orps are BIG girls, so maybe the powder isn't enough? Any advice much appreciated!! P.S The orpgintons live in a wooden chicken house alone, the other chickens live in a plastic one - could it be the housing? I treat the wooden hen house with pest spray once a month.