The unicorn is an equine that has a horn on its forehead. The horn gives it a dressage bonus.
To successfully give birth to a unicorn foal, both of its parents have to be unicorns of the same breed, and the mare must be covered at an exact time decided on by each breeder exactly.
If this is the case, you have one out of 5 chances of giving birth to a unicorn. To cover a unicorn for the first time, you must wait at least 10 hours after its birth.
You must also wait at least 10 hours between any two coverings of the same unicorn mare.