ridecowgirl,
I've never dealt with lice on horses myself, and so I looked it up, all I could really find was that it can be treated with commercial lice treatment, like Farnum's Lice Duster III. I'm sure there is someone else on here that has had to deal with this before, and has some better advice than any I might have, as I seem to have none

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I got your note, and the other mare that was in the trailer wreck is fine. I'm going to be working her for the owner a little now in the evenings next week, just to get her back in tune.