breeding stallion; stud horse; stud
Specifically a male horse kept for breeding purposes, used in horse racing and livestock contexts.
This farm raises several excellent breeding stallions.
The offspring of that stud horse won a graded stakes race.
A more general term for a stud horse, but 種牡馬 is the technical term used in horse racing and breeding registries.
Compound of 種 (しゅ, 'seed; breed') + 牡馬 (ぼば, 'male horse'). The reading ぼば for 牡馬 is a less common Sino-Japanese reading; 牡馬 is more often read as ぼば in technical equine contexts.