I've seen Eastern European and North African instruments (of the bowed, one -or two string variety, mostly with skin tables) strung with horsehair; not individual hairs, of course.  Better than human hair, I'd have thought, but then I haven't tried the latter.  There are a lot of very similar instruments around Central Asia; these are traditionally strung in much the same way, but often with silk.  Idiochord tube zithers -which go back a good long way- apparantly have "strings" of bark.

Malcolm