domestically bred horse
Refers to a horse bred within the country, as opposed to an imported horse. Used in contexts such as horse racing, breeding, or agriculture.
This racehorse is registered as a domestically bred horse.
外国産馬 means 'foreign-bred horse', the opposite of 内国産馬.
Compound of 内国 (ないこく, 'domestic') + 産 (さん, 'produced') + 馬 (ば, 'horse').