The cow had an awkward time moving through the doorframe, but they managed and made sweet love until falling asleep.
The next morning, Brent gazed over at his new sleeping cow-love. Her glistening, soft, supple bronzed skin caught some of the morning sunlight beams. He took a quick look at his alarm and sighed in contentment - he had the week off school and could enjoy a week with his new lover. He got up to make some coffee and breakfast. He wasn't really sure what would be appetizing to his new lover... cows ate grass, corn, oats, hay, not meat. He decided to go vegan this morning. He soon heard the gentle mooing and tip taps of his bovine lover.
"Good morning." Brent said with a chipper attitude, "I was just about to make breakfast. I wasn't sure what you'd like to eat."
The cow blinked her eyes and then sat back, revealing her human breasts.
"Wait... are you lactating?" Brent asked, "You want me to make some french toast or something?"
The cow mooed in agreement. Brent chuckled and got to milking the cow. He saw something like this before and started to work her up, to his surprise she did begin to produce milk - apparently this was very pleasurable to the cow and she threw her head back in pleasure. Brent got a cup of human... cow... milk? He tasted it, sweeter and creamier than cow's milk. Warm, too. He was used to cold in the fridge. He whipped up the rest of breakfast in short order. He served the cow, a plate of french toast with berries. The only thing betraying it from being complete vegan was the cow's milk she wanted to be added. They ate together.
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Over the course of the day, Brent noticed something off about the cow - besides the human body parts. He wasn't sure exactly what it was. She seemed smaller than he remembered. Her eyes seemed brighter and more human, more quizzical and curious. She seemed a little more confident. Brent didn't have much time to notice any changes as they continued to fuck and suck the time away, only taking breaks for rest and eating. The cow was madly in love with Brent, and Brent with her.
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The next day, something was definitely different about the cow. Her eyes had changed to blue. Her rear-end was rounding off and her front legs were shortening. She seemed to struggle to walk on all four and attempted to walk bipedal, but she was too tall and was incapable of that as well. Not that she needed much movement, anyway. They mostly spent the day in bed together.
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Finally, Brent awoke after the cow already had. He heard a soft gibberish singing in the kitchen. He darted up. Could it be? He emerged into the kitchen. There was his cow girlfriend... her size had shrunk enough that she could stand upright and she had developed enough leg muscle and skeletal ability to walk upright. She was seemed otherwise unchanged, same breasts swinging proudly where a cow's udder would be, same dainty soles at the end of her legs, same soft skin. His eyes scanned, her front hooves had become dexterous enough to manipulate pans and spoons between the cleft in her hoof. She had long tumbling locks of hair falling onto her cow-head.
She finally noticed Brent and waved. She made a gutteral moo gibberish noise. Her mouth wasn't formed well enough for proper words, apparently.
"Hello!" He said, "You look so... different! I like this new you."
The cow giggled. She put the food in front of him - french toast. He grinned and they ate again.
The cow's new human size and bipedal ability let them explore new sexual positions. Doggy style, traditional missionary, missionary with her on top (and not crushing him), every position in the Kama Sutra. Brent was excited for what changes awaited them the next day.