This is the second outbreak this summer of lice on my hens. I treated them with dri-kill dust powder and repeated it two weeks later. Seemed fine for a few weeks. Now I found more on them,not in their coop only on them.Is this going to be a normal procedure every 6 weeks to dust them? Is this because they free range and have contact with other wild birds like sparrows ect? does anyone else have a repeated lice problem...and would it keep lice off them if I kept them from free ranging and only confined them to a run??thanks