a horse whose tail has been cut short (trimmed straight across or docked), usually for appearance or practical reasons.

尾を短く切られた馬（外観や実用上のために尾を短く整えられた馬）

(Racing/colloquial) An untried or inexperienced racehorse; a horse regarded as inexperienced or not yet proven.

（競馬・俗）経験の浅い競走馬、未試走の馬（まだ実績のない馬）

to cut or trim (a horse's) tail short; to make (a horse) into a bangtail.

（馬の）尾を短く切る、尾を整えて「bangtail」にすること

having the tail cut short; described as a bangtail (often used before a noun).

尾が短く切られている（名詞の前で使われることが多い）