Messy Beast's learned treatise on horsies includes a fascinating section on long-maned wonder horses, exhibited at carny sideshows and the like, with their flowing, lovely locks. Let the broniegasm begin.
Circuses and sideshows often invented exotic stories about their exhibits. For example, exceptionally hirsute men were exhibited as "lion-faced men" or "wild men" along with tales that they had been captured in a remote country, were wild and ate raw meat. Despite the legends that the "Oregon Wonder Horses" had been captured from a legendary wild herd, they appear to have been bred from Clydesdale, Percheron draft horses, possibly with some Andalusian blood as well. Excessively long manes and tails would have been a severe hindrance in the wild and needed a lot of care in a domestic situation.