noun
teaser stallion; test stallion
In horse breeding, a stallion used to check if a mare is in estrus before introducing the intended sire.
牧場では、繁殖期に当て馬を使って牝馬の発情を確認する。
At the ranch, they use a teaser stallion during breeding season to check if the mare is in heat.
noun
stalking horse; spoiler; decoy candidate
Figurative use in politics or competition: a person or thing put forward to draw attention or test reactions, often to benefit another. The 'spoiler' nuance is when a third candidate splits the vote.
彼は選挙で当て馬として立候補したが、本命候補の票を奪う結果になった。
He ran in the election as a stalking horse, but ended up taking votes away from the front-runner.
その新製品は、競合他社の反応を見るための当て馬に過ぎなかった。
The new product was merely a stalking horse to gauge competitors' reactions.
Specifically a 'stalking horse candidate' in an election, a common compound using 当て馬.
Compound of 当て (ate, 'to apply, to hit against') + 馬 (uma, 'horse'). Originally a horse-breeding term for a stallion used to test a mare's readiness; later extended figuratively to politics and competition.