Here is a list of Hololive and their Horses

Aqua - Suzuka
Botan - McQueen
Miko - Urara
Pekora - Mayano
Polka - Grass
Kanata - Suzuka
Fubuki - Oguri
Rushia - Rice
Suisei - Opera

Who else?

List may be inaccurate and/or subject to change.