You whicker happily as you see the results of your changes - the blond, muscular youth is a perfect match for the magnificent Clydesdale stallion body that sweeps down from his waist. His eyes are wide and dazed as he clutches at your mane - he hasn't yet realized that he isn't the same below any more.
Before he has regained enough of his wits to figure things out, you are amazed to feel him stiffening again inside you! The transformation seems to have recharged him sexually, and he starts thrusting all over again.
If anything the second time is even more intense than the first - his Clydesdale cock is a better match for your draft horse mare cunt, and the pressure of his massive equine body on your rump and back adds a sense of being dominated.
You don't want him to change any more, but instincts and horse mentality are harder to control this time. Are you starting to think like a normal mare? The horse in you wants a powerful normal stallion as a mate, the human in you wants to keep the boy a centaur.
Then the orgasmic pleasure takes over everything as Clydesdale balls empty themselves into your already-flooded insides. When the last hot gush has come inside you, you manage to clear your head to look back.