"Alright, I'll do it!" yelled Natalie, as though she'd been forcing herself to keep quiet for hours.
"You sure about this, sis?" asked Emily, worried for her sister.
"Sure! I'd love to get closer to my babies." she said, referring to the horses in the ranch she tends to every day. With that she opened the Horse Serum vial, poured a spoonful and drank it in one gulp. She shuddered a bit and crinkled her nose.
"Yuck, tastes like medicine." she complained, sticking her tongue out.
"How do you feel?" asked Mary.
"I'm feeling pretty good, nothing different yet. I'mma go out and spend some time with the horses see how good this stuff works." and with that she marched right out through the front door into the ranch.
"Alright, I'm next!" yelled Mary.
In about ten minutes, Natalie had reached the farm's stables. There she greeted the horses as she did every morning and threw some wheat in for them to eat. She opened the stable doors and let them out into their pen in to get some exercise. One of the mustangs, Flint, as he was known refused to leave his stall.
"C'mon Flint, what're you waiting for? Brand new day, perfect to go stretch out them strong... black legs of yours." Natalie said, feeling a bit light headed. She began to, without control, walk inside Flint's stall. She began petting the fur on the back of his head.
"What's wrong Flint, feeling a little lonely? You know, you're quite the guy, I'm sure there's a mare out there just waiting for someone like you." she said as she kissed Flint on the back of the head.
"Oh god, what am I doing?" Natalie yelled, running out of the stall as fast as she could, tripping on a pile of hay. She looked down at her feet and her mouth gaped in awe and fear.
Her toes had merged into hooves where her feet once were, with brown fur spreading across her legs. She began to scream for help, but she was too far out to be heard by any of her sisters. It was then that she began to experience an alien, sensual feeling at her waist below her stomach. Two nubs grew on both sides, forming nipples and eventually growing out into a small mare's udder right below her abdomen. Her ordinary breasts began to swell up, growing to a C-cup. Her spine lengthened, and at the base, she felt it growing into a lush, brown mare's tale. As she pushed herself up, she felt the fur spreading through her body, each new strand resulting in an arousing, almost ticklish sort of feeling. She moaned in pleasure as her face began to stretch forward, her skull shaping itself into that of a horse. Before long, she began to use her new, furred hands to massage her womanhood. Her ears pointed upward, and thinned themselves out, like a horse's. By the time the transformation was done, she salivating from the orgasmic feelings of the transformation, her new equine vagina dripping with fluid as she sat leaning against the stable wall.
"Oh... oh... that was... great..." she moaned. She stood up the best she could on her new hooves. Her entire body was covered in delicate brown fur. Her hands had four fingers each, including a thumb, nails turned jet black. Her legs looked like that of the hind legs of a horse, combined with a human's legs. She had grown about half a foot taller, and she had grown a bit of muscle in her arms, enough that she looked like she could carry a substantially larger amount of weight than before, but not so much as to hinder her nimble stature. She looked like she had been a natural born runner, and that essentially is what she had become, her tail swinging behind her.
"Well, I guess this is... different. Should I tell the other girls? I think I could get used to this." she said feeling her newly formed breasts.
"What now?" she asked herself.