Zombie and skeleton horses do not spawn naturally and cannot be spawned via gameplay, but can be spawned using commands when cheats are enabled, or by operators in multiplayer games.
Zombie and skeleton horses each have two spawnable versions, a tamed and an untamed version. The untamed version cannot be tamed. The tamed versions can be saddled and ridden, but not armored. Leads also cannot be attached to any version, and they cannot be fed or bred. They all spawn with 52 (Heart.svg × 26) health, which is much higher than other horse variants.