This is an insanely cool concept hook and really good execution, I enjoyed playing this immensely! Your 2D art assets are gorgeous and fit the overall vibe really well (+ honorable mention to the horse legs lifting animation in the minigame, probably an odd thing to notice but horse animation is quite difficult and that felt very well done^^) and having to jump between horses to care for them as quickly as possible worked great for engagement (difficulty-wise it felt doable too). I saw that you could feed the horses with meat aswell but never got to the point where they demanded that, is there a further mutation step after growing a second head? xD
(Also I guess that is not the plan, but should you ever decide to keep working on this further, I am definitely interested in where it would go:))
Excuse the long comment, you did great work!