A horse is a large four-legged animal that is frequently used as a beast of burden by humans. Horses originally evolved on Earth, and like humans have been transplanted to several other worlds in the Milky Way. They are usually used to transport goods and people, as well as draft and working animals.
The Shavadai on Simarka use horses as mounts. (SG1: "Emancipation")
Gairwyn is seen riding a horse, implying the Asgard transplanted them to Cimmeria as well as humans. (SG1: "Thor's Hammer")
The Hak'tyl Resistance also used horses and brought some through to Stargate Command after they abandoned Hak'tyl. (SG1: "Sacrifices")