Horse lice?

Hi, I have a 1 yr old miniature horse who has lice on him. I tried putting vinegar and brushing the bugs out, and it seemed to work. However, I think that the barn is still contaminated because although all this morning and afternoon he was free of lice, in the late afternoon I noticed more lice on him. How can I effectively get rid of the lice on him and disinfect the barn? Thank you!