You neighed a little when you looked back at Steve and stomped your hooves a little. You could tell that he was having a hard time resisting as he started to grow in size, his chest barreling out a little as his clothes strained against his body. He didn't even seem to notice or care as he pushed his pants down and she saw his growing horse cock slip out of its newly formed sheath.
You whinnied a little as your human mind protested what was going on, you weren't an animal, you were a human being! But your mind was slowly descending into the horse instincts as it was begging to be mounted by the stallion. Your human side tried to protest, but you readied yourself to be mounted by the stallion.
You looked back at your transforming boyfriend as his face was pushing out to form a muzzle. He could smell your heat, but it was as if he didn't even realize what was happening to him. He stood up on his tip toes and positioned the growing tip of his cock at the mare's slit, he let out a neigh and you realized it was too late for both of you, so you might as well make the most of it.
You finally gave in and closed your eyes as the stallion started to lean on your back as he grew out into his new Horse form. You finally let out a loud whinny as he thrust into your waiting vagina and you shivered a little as he started to thrust in and out of your vagina and you let out another whinny.
As you felt the strange in-human cock pump in and out of you and shivered as you felt it rubbing against the insides of your body. There was something, strangely exciting about the feeling as he thrust faster and deeper into you and his weight settled over your body as his body finished its transformation. You whinnied as you felt his cock grow longer and thicker as it thrust faster into you, you started to enjoy the feeling.
Your horse body shivered with joy as you felt the stallion's balls slapping against your hindquarters. You neighed loudly, and you had to admit there was something wonderful about it as it sent waves of pleasure through your body. This wasn't like human sex at all, it was more enjoyable, more animalistic and it was amazing!
Your mind was completely overtaken by the horse instincts as you moved with the thrusts. Finally you felt your vagina start to clamp down on the cock as you felt his balls churn and he thrust in one last time, his cum spurting out into your waiting vagina as your muscles clamped down on his shaft, drawing out as much of the wanted seed into you.
You breathed heavily as the stallion pulled out slowly and dismounted you. You whinnied lightly as you felt the mix of juices drip out of your vagina and down your hind legs a little. The stallion nuzzled you gently, and somehow you knew that this was where you were meant to be.
As your human mind re-asserted itself you looked into the eyes of the new Arabian Stallion and frowned a little. There was no longer any sign of human intelligence in his eyes, the process had completely turned him into a horse in mind and body.
"Well done," the attendant said as she walked into the stall and put a halter on the stallion's muzzle and brought him into the stall next to yours. "So, did you enjoy that?"
You nodded your head a little and she smiled a little that. "Alright, good, perhaps we can get more studs in here with you," the attendant said and winked. "I think you're going to have a lot of fun here Jennifer, think of all the studs you'll make, all the foals too. Welcome to the world of horses."
She headed out of the stall and closed the door after setting some food out for you. You looked over at your transformed boyfriend before leaning in and eating.
You were a horse now, you might as well get used to it.