Diane strode out the house, not caring that she was naked for leaving a trail of cum in her wake. Her enlarged nostrils picked up a friendly scent, and she followed it. Her hooves clopped against the pavement, and soon she was running toward the smell. Her hands felt uncomfortable, but she ignored the sensation. All Diane could think about was finding the source of the enticing smell.
As she ran, her hands melted away until she had shiny new hooves. Then a crack in her hips made her cry out in pain. Diane was forced to the ground, and she stopped to breath for a moment. The smell once again assaulted her nose, and she ran, now on all fours. She was faster, and it only took a few minutes for her to arrive at a farm. There, she was lead by the smell of a mare in heat in the pasture.
Diane leapt over the fence, and approached the female. She sniffed the horse's rear, and snorted into it. Air teased the mare's dripping cunt, and she whinnied. Diane understood it as a direction to go for it. So she did. As she mounted the mare, her face finished stretching out into a horse's snout. Long hairs began to push out from her tail bone, and soon Diane had a proper horse tail swishing behind her. Her body mass doubled, even tripled as she expanded.
Fur spread up her body, and lengthened once it reached her growing neck. Her mane continued to grow as her neck stretched to its full three foot length (give or take). Diane had some trouble inserting her penis into the mare, as she'd never done so before. But one the head found the mare's lips, Diane whinnied in pleasure and didn't hold back.
Her cock plunged into the horse's lips, and the mare cunt tightened around her shaft. It was unlike anything Diane had ever experienced. She knew it was wrong, but it felt so damn good. She slowly pulled back, loving the way the mare's vagina felt rubbing against her cock. Then thrust back in. Over and over, her balls slapping against the mare's ass. Her own ass was covered in hair, and her asshole large and black. Heat radiated from it, and soon Diane took the biggest shit of her life as she continued to fuck the mare.
"This is so goood" she thought distantly. Her mind was a million miles away. All she could focus on was reaching her orgasm. The mare's pussy clenched again, and that's all it took for Diane to shoot spunk into the mare's hole. She snorted in pleasure as the last of the stream was sucked up by the mare cunt.