Flavor preferences in horses have been studied a few times to see what they like best. This has commercial applications as flavorings are often added to feeds and especially supplements to mask distasteful components and enhance palatability.
There seems to be some sex difference in preference with mares preferring sweet and carrot flavors in one trial, as against stallions opting for sour apple flavor.
In another comprehensive experiment the results in order of preference were:
Fenugreek> Anise> Banana> Cherry> Rosemary> Cumin> Carrot> Peppermint> Oregano>
Garlic and Cinnamon came at the bottom of the list with no preference for them shown over the plain cereal mix offered.