Minecraft wiki entry for Horse, associated text: Bred with a horse: Breeding two horses produces a horse foal. Usually, the new foal has the color and markings of one of its parents, although there is a 13/45 chance of having a random color/markings (which may still end up being the same as one of the parents).
Bred with donkey: Cross-breeding a horse with a donkey creates a mule foal. Mules cannot breed. This unlocks the Artificial Selection achievement.‌[Bedrock Edition only]