The next morning when Jenny woke up she could tell something was wrong but she couldn't quite put her finger on it. She got out of bed and ran herself a hot bath, then sank down into the water to relax hoping the feeling would go away.
As she lay there Cynthia came in. "Did you enjoy yourself yesterday?" she asked.
"Umm... yes..." Jenny said with a blush
Laughing Cynthia said "Oh don't be embarrassed if you enjoyed it do it as often as you like!"
-----
Later that day remembering what Cynthia had said Jenny slipped back into the barn. She stood staring at the pony and it's very large cock that had become very hard when she walked in. She shuddered than looked around to see if anyone else was in the barn. "I shouldn't" she said to the pony "but you felt sooo good yesterday. I just cant help it."
She took off her clothes and walked into the stall. Slowly she bent over a bale of hay revealing her already sopping wet sex to the pony. With out wasting any time the pony rammed his very hard cock inside her vagina. She let out a startled scream that quickly became a pleasureful moan as he slammed in and out of her. She could feel her tight vagina tightly hugging the pony's member as it slid in and out and every time she seemed to feel more and more pleasure. With a shuddering whinny she felt the pony squirt his massive load inside her opening and she felt her stomach swell with his seed.
Carefully she got dressed and went back to her room to take a bath and think about what she had done. After she got back into the tub she was startled to see that her stomach was still slightly swollen. Thinking it was just her imagination she put on a night gown and went to bed.
Late that night she awoke in a cold sweat, as she lay on her bed panting she could feel the heat radiating from her sex. She pulled up her night gown and was startled to see that the lips of her Vagina were now larger and jet black. With a trembling finger she reached down and touched them and shivered as a jolt of pure pleasure raced through her. Suddenly all she could think about is what the pony's penis would feel like penetrating those dark folds. Scrambling out of bed she ran down to the barn and tore off her night gown and threw herself back over the hay bail.
The pony was at first startled by her sudden reappearance in the stall but when he caught a wiff of the strong scent coming off her dripping vagina he scrambled up and was instantly on top of her.
As his penis penetrated her vagina for the second time that day, it was all she had hoped for. With the new sensitivity in her vagina she could feel every inch of the penis as is slid into her. She could feel as it touched the entrance to her womb and she relished every time it slid in and out of her. Moaning with pleasure she hit a climax higher than anything she had felt before and screamed in pleasure as the pony continued to thrust in and out of her. After a few minutes she felt the pony cum hard deep inside her and felt her stomach swell even more with the new load of seed.
The next morning she woke up laying in the scattered straw in the pony's stall. Confused as to how she got there she slowly got up then realizing she was nude, ran to her room. Once there she began to notice that she felt a little different and that her stomach was now bulging out as if she were pregnant.
Quickly she ran into the bathroom and looked at herself in the mirror. She was startled to see that her Vagina was even more swollen and was still a jet black, but now she could see that her breasts were bigger and fuller with dark nipples. As she stood there Cynthia walked in.
"Have you and the pony been having fun?" she asked smiling
"Whats happening to me!?" Jenny yelled
Smiling Cynthia replied "The owner of this house has various clients that buy rare and unusual things from him. One of the things they asked for was Anthopony girls. You are the first of them thanks to the chemicals we gave you when you got here. Your children," pointing at Jenny's bulging stomach "will be the ones he offers up for sale."
"What!?!?!" Jenny screamed "You cant do this to me!"
With a laugh Cynthia said "We aren't my dear, no one made you have sex with the pony but you did anyway. And every time you have sex with him you will change a little more until you are totally an anthropony that will fulfill your owner's every sexual desire."
"I wont do it anymore!" screamed Jenny
Laughing Cynthia just shrugged "If you can resist it go ahead, you havent changed too much... yet... your children you are already pregnant with will only change as you do. If you can resist they will only have your current attributes. But if you can't..." with an evil laugh she turned and left the room.
Jenny sank to the floor and started to cry, but as she sat there she could feel the heat rising in her sex again.
"NO! I wont do it!" she screamed
As the hours dragged on she got hornier and hornier until she found herself standing outside the pony's stall with no recollection of how she had gotten there.
Staring at the pony she thought to herself 'one more time wont hurt... and it will feel soooo good...'
Slipping into the stall and out of her clothes again she submitted her self to the pony who was more than happy to take her again. Screaming with pleasure she once more felt him thrusting deep inside her. Again she felt him blow a large load of seed deep inside her and felt her stomach swell a little more, only this time she also felt a sharp tug on her ears and base of her tailbone. After the pony pulled out of her she slowly felt her head and felt the beginnings of a pair of Horse like ears where her normal ones should be. Cringing she reached back and felt a small tail coming out of her backside.
With a startled cry she curled up in the corner of the stall and began to weep.
----
Cynthia stood in the kitchen and smiles as she looked at the security monitor showing Jenny in the barn having sex with the pony again. When she saw the ears and tail she laughed and turned the monitor off...