"Come on big boy, you know you want this," Jessica said as she wiggled her now horse butt at me as you moved in closer. "You know you want to take me stud, you want to breed me like the mare I am just as much as I want you to breed me."
You couldn't resist it any longer as you mounted the mare as you placed your forelegs and hooves on her back and pressed the tip of your now fully equine cock against her vagina as your instincts were encouraging you to mount her. The mare was in heat and you wanted to get her pregnant just as much as she wanted to carry your foals.
Something at the back of your mind pressed at you briefly as you couldn't remember Jessica not having fur or a leathery vagina, but the smell was driving you crazy. You didn't care anymore, she was your mare and nothing else.
You couldn't resist any more as you thrusted deep into Jessica's vagina. She moaned loudly as she threw her head back as you thrusted faster and deeper into her. You couldn't believe how good it felt to mate with this mare as the last of those doubts slipped from your mind and both you and Jessica whinnied as your muzzles formed perfectly.
You thrusted faster and deeper as you neighed, your instincts were getting stronger and more overwhelming as you kept going. You were now nothing more than an animal, driven by the instinct to mate and spread your seed with as many mares as you can, and something at the back of your mind told you that to do that you needed to transform more women.
That same thing told you that you needed to cum inside the mare, you wanted to impregnate her, but more that it would make this permanent. Make what permanent? You were a horse, you hadn't ever been anything else other than a stallion, and as you thrust one last time into Jessica you both neighed loudly as you coated her insides with your seed. Her vagina clamped down on your cock and drew out as much of your cum as she could.
You pulled out and nuzzled the mare that was now your mate. You swished your tail and the two of you started to eat while the other two horses watched them.
Unlike the two new horses, these two remembered who they once were. It was always a strange experience for them to see people being transformed, but they had gotten used to it, and even come to enjoy welcoming new horses into the stables.