You let out a loud gasp as a searing heat suddenly washes over you, spreading from your dick and balls to your entire body and sinks deep into your flesh, quickly giving way to a swelling sensation and a sense of.... power. Sure enough, as you watch, your previously lithe frame is becoming bulkier and brawnier, packing on more and more muscle mass by the second. Within moments, you're sporting a set of muscles that wouldn't look out of place on a bodybuilder, with arms that you could crush apples with and abs that you could grind meat on.
As your body bulky up, your arms and legs feel like they're being stretched out, your torso becoming somewhat wider and sturdier to carry your newfound musculature, and you gradually inch upwards and grow taller and taller, going from six feet two inches to 6'3", then 6'5", then 6'10", then finally 7'1". A faint pressure builds in two spots on your forehead, and two small upwards-curving bull horns burst out from the top of your head, and a thin tail covered in sandy hair and tipped with a tuft of longer fur pushes its way free just above your new meatier ass.
And finally, an almost orgasmic feeling of warmth blooms within your cock and balls, and your package immediately begins to swell larger and larger. You let out a groan as your balls inflate larger and larger, shooting past the size of oranges to nearly eighteen inches across at least and practically sloshing with what feels like literal gallons of cum. Not to be left out, your penis rapidly swells to be longer and longer, wider and wider, until it's almost three feet long and eight inches across, with a head the size of a large softball that's practically throbbing with blood.
"Wh... what... what happened?" You pant out in equal parts lust and shock, staring openmouthed at your monstrous cock. "Did you... do this?"
Bessie smiles and nods; despite your newfound size, she's still much bigger than you, and her weight on top of you is still too much for you to push off. "I did, John. I know that you like big women, and that you always wanted to be a bit bigger yourself, so I decided to... enhance your body a little bit so that you'd fit your dream body... not to mention mine." She grins and lies down on top of you, kissing you on the cheek. "Do you like it?"
"I... I have to say, I do." You reply, your head still swimming from the combined sensation of your orgasm and transforming into a bovine Adonis. You smile at Bessie, and you lean forwards and kiss her full on the lips. The bovine beauty is surprised at first by your forwardness, but as she realizes what you're doing, she melts into the kiss with a deep moan, her still larger tongue swirling around yours and her great soft breasts and belly pressing down onto your own toned chest. After several long moments of kissing, Bessie finally pulls away from the kiss, her immense chest heaving with lust.
"You're the perfect mate for me, John." The cow behemoth pants out, her pelvis grinding against your immense cock. It seems that she's up for another round...