Bangtail

1851, Turning Out a Bagman: A Legend of Brighton Downs, in Charles Dickens, William Harrison Ainsworth, Albert Smith Bentley's Miscellany, Volume XXIX, page 259, Two lean, ewe-necked, clipt chestnuts, tucked up in the ribs, with hard work and bad feeding, but with such flowing bang-tails as at once stamped them in the eyes of our friends as “ out-and-out ” thorough-breds—were led up and down by John. […] The bang-tails, no doubt, supposing themselves out for their usual “airing,” put themselves in the regular side-long position, and struck at once into a sort of hectic canter ; a particular movement, peculiar to Brighton bang-tails, and adapted to the most innocent equestrian.

Source: wiktionary

1903, Tom Collins (Joseph Furphy), Such Is Life: Being Certain Extracts from the Diary of Tom Collins, 2004, page 68, "And did you see a dark chestnut horse; bang tail; star and snip; white hind feet; saddle and bridle on?" I asked.

Source: wiktionary

Lennan held the black horse — a bizarre little beast, all fire and whipcord, with a skin like satin, liquid eyes, very straight hocks, and a thin bangtail reaching down to them.

Source: wiktionary

Once we get the herd we can set up relays to keep the bangtails movin' as we go.

Source: wiktionary