The filly before you notice that you stopped approaching and huff impatiently, and start clopping back a few steps until she is exacly before you. Your eyes wander again to her waiting lips that with a new wink make your lust uncontrollable, your hand reach for your cock and for a moment of lucidity you marvel at the new lenght and thickness before you position yourself behind her with the tip of the cock pressing against her wet vaginal entrance, and with a mighty thrust you shove you throbbing manhood in her wet folds, parting her black sex with your shaft, savoring the way your cock continues to penetrate the excited mare.
Your thought are muddled as you continue to hump her slick lips, with repeated motion you continue to pull out and thrust back inside and the mare's bottom continues to produce meaty slaps as his hips met resistance.
You grunt as you start to hump faster and faster and you realize that you are near an incredible explosion; you trow back your head and whinny as your body shook and your semen shot up inside her, a second before her vaginal walls clamp your throbbing cock and she came alongside you. You thrust again and you came a second time, and only now you realize that you are utterly exausted, your shaft pull out of her puffy folds as the juices of your mating starts to drip on the straws of the floor. The mare gives you a once-over before is satisfied and then nuzzles you affectionately.
"Enjoyed the ride?" the attendant whispers to you with a massive grin on her face, then reach behind her and skillfully wrap an halter arount your new muzzle. Your rising panic as you realize that you have hooves and a tail is entertaing to her, and as she herd you to your new stall, your new home, she whisper again "Now that you have become a stallion of our stables i expect your cooperation on converting more visitors, exactly like the mare that converted you... Maria became a filly almost four years ago and in time she started even to enjoy changing new stallions like you, i even have a tally of how many visitors she changed i believe... Don't even bother to escape: the transformation is permanent because you came inside her, it would be a shame to sell you, we collect the best stallions between the trasformed to keep in the zoo to mate, and we had a lack of capable stallions. Tomorrow we will begin your training"
My new ears drop as i understand that there is no turning back and i will be a horse for the rest of my life, then she bring me in the stall and closes the door "Goodnight my strong stud, we have great plans tomorrow, great indeed..."