yearling; one-year-old colt
Specifically refers to a horse that is one year old, often used in equestrian or breeding contexts.
当歳駒の競り市が開かれた。
An auction for yearlings was held.
牧場で当歳駒が元気に走り回っている。
Yearlings are running around energetically at the ranch.
Formed from 当歳, an animal born in the current calendar year, and 駒, “foal”; it originally denotes a foal of the current year.