Jess ran her hooves over her breasts, cupping them and feeling just how full they were. They were so heavy... Suddenly there was an ache building behind her teats, and Jess let go of her breasts. The ache didn't stop, it only got worse. Mary had been watching her friend curiously, and realized what was wrong.
"What's, ow, wrong?" Jess winced, arms wrapped around her waist. Which was hard since her torso was lined with eight piggy breasts. Mary was going to explain, but the milk dribbling out of Jess' teats did the job. Jess saw the liquid pouring out, and look to Mary.
"Uh, can you...?"
"I thought you'd never ask." Mary said, almost seductively. She didn't hesitate to walk up to Jess and latch onto one of her teats.
Jess fell against the bed, her body overcome by the pleasure. It was like Mary was eating her out (in a way she was). The sucking motion and the feeling of the milk exiting her body, Jess moaned in pleasure. Using her hooves, she began to milk herself while Mary switched from one teat to another. She too was thoroughly enjoying this, as the milk spread a warm feeling throughout Mary's body.
Neither noticed that the more milk Mary ingested, the more obvious the changes to her own body became. It started with her ears, which drooped and became pig ears. On her chest, her breasts returned but much larger. F cup breasts with long four inch teats like the one Mary was suckling on.
When she finally felt full, Mary pulled off the teat, a very loud and wet "pop" as she did. She leaned back and sighed. Jess, still flat against the bed, was lost in the pleasure. Her hooves kept milking the other teats Mary hadn't sucked dry.
"That was incredible." Jess said. Mary nodded, and looked down at her friend. And at the same time, saw her transformed body and gasped, drawing Jess' attention. They both stared aghast at Mary's transformation. Obviously there was pig vial in Jess' milk, which begged the question to both. What would happen now if they drank each other's milk?