You snorted as you moved in and sniffed at the transforming woman's folds. Your instincts could already tell that she was in heat as she barreled outwards, her body becoming more and more like the perfect mate for you. She let out a whinny when she felt your tongue probe her depths as the group stopped in mid step.
"Stop him!" Vicky managed to get out as her face stretched out with her ears migrating to the top of her head. "Please don't let him... NEIIIIIGH!"
"A shame Vicky, but the boss wants two more Broodmares not a stud," the attendant hat had talked to you said with a smile. "And you've been volunteered to take Princess' place, and I'm sure you'll enjoy it... eventually."
She let out a whinny as she felt you on her back, your shaft's flared tip pressing against her flanks. You looked over at Jessica where the white mare was now grazing. She looked up at you with what looked like a slight nod, you needed no further prompting as you thrust forward. This time your aim was far more true as your shaft plunged deep into her folds, you felt them start to constrict around your cock as you stretched her out with each thrust.
Vicky's eyes went wide as she felt her changes start to accelerate. The last of the fur covered her body as her chest barreled out. She felt a strange sensation between her hind legs as her breasts migrated down to become her teats. She threw her head back and whinnied as she felt you thrust into her again, this time hilting her as your balls slapped against her a little. Despite herself, she found herself enjoying it as she was filled completely, her body now completely equine.
You couldn't believe how natural this felt now, how had you ever even considered being human again? With each thrust you felt more and more confident in your new body. You picked up the pace as the rest of the attendants watched with a smile as you mounted their former superior. The strange sensation and sounds from the mating between the two horses was driving you wild. You felt the mare's muscles contracting around your shaft.
Finally, you threw your head back and neighed loudly. You once more felt your balls twitch as your seed spurted out into Vicky's womb. By now Vicky had completely surrendered to the animalistic pleasure. You finally pulled out of her as Jessica moved on the other side of you. You gently nuzzled both your mares.
"Well, well, aren't you three perfect?" The Attendant said with a smile as she patted all three of you on the nose. "Come on, time to head home."
They led the three of you back to the Stables. Back home where you would spend the rest of your lives serving the Zoo.