The 'Check breed' button in the stable was enhanced and it can give you the information about the compatible breeds.
If you leave the Mare breed as 'Any' and click the 'check' button, that will return a list of the compatible breeds.
For instance if you check what breeds are compatible with Andalusian, the result will be:
Andalusian can breed with mares of the following breeds:
American Quarter Horse, Friesian, Percheron, Andalusian, Donkey