The male parent of a domestic horse is called the sire.
In horse breeding, “sire” identifies the father of a foal, while “dam” identifies the mother. These terms are used for both thoroughbred pedigrees and general breeding records. A young horse of either sex is a foal, so “foal” describes age rather than parentage.
A stallion is an adult male horse that has not been castrated, and a gelding is a castrated male horse. A stallion may be a sire if he fathers a foal, but the words are not synonyms: one describes reproductive status and the other describes parentage.
Pedigrees record a horse’s sire and dam because inherited traits influence performance, conformation, health, and breed identity. Thoroughbred racing has especially formal pedigree traditions, with recognized studbooks tracing ancestry over many generations. The same vocabulary also appears in breeding records for ponies and other equids.