Henry led David and Stella the jenny down a darkened corridor within the stable lined by many stalls. From the sound and smells, he could tell there must be dozens of animals behind the doors.
"Let me show you one of our fine stalls for a moment," Henry said, motioning David through a door.
David stepped in, a bit hesitant as he had never been in a stall before. A single lightbulb hung from the very high ceiling, and the only window in the room was on the door David had just stepped through. The air hung heavy around him, as there was little circulation. "No offense Henry, but this place is a dump.."
Just then he saw Henry guide the jenny into the room and slam the door shut. A sliding sound and thud signified that Henry had locked him in with Stella. "What the hell are you doing?!" David ran to the window and saw Henry standing there laughing. "Let me the fuck out of here damn it!" David banged on the door but it held solid.
"Hehe.. I don't think so David. Don't worry, you'll come to see I'm doing you a major favor here."
David banged on the door again, "You god damn maniac, I'm calling the police when I get out of h...". David stopped beating the door when he noticed his arm seemed a bit darker than normal. He rubbed at his forearm and was shocked to find a thing layer of rough fur across it. A quick check over the rest of his body revealed the same - his legs beneath his shorts and both arms had a light covering of fur, and even worse, it seemed to be thickening and growing. Just then David remembered that strange drink he was given earlier...
"What was in that drink?! What the hell's going on??"
Henry chuckled as he turned to walk away, "Just take solace in knowing that in a short while you'll be having the time of your life David... everyone who comes here does..."
David barely heard what Henry had said before he left, he was too concerned about what was happening to him. Already he had broken into a frantic sweat, and as he lifted his shirt up in the front to glance at his belly, he was dismayed to find even more fur. Thickest around his happy trail, he stretched his shorts open with a finger to glance down between his legs, only to find his member had grown strikingly erect - not only that, it too seemed to be darkening... and as he watched a pouch of skin formed around it and attached itself to his belly, forming what looked to be a sheath. David shreaked and let his pants cover himself again, only now they felt much tighter.
David frantically glanced around the room, looking for a way to get out. He noticed Stella standing there in the corner of the room, her rear turned toward him, her tail swaying side to side. Why did Henry leave her in here with him? It was then that the sheer realization hit him. Henry had told him that he had just acquired a new male to mate with his jenny's, and he had hired David to assist. What Henry had in fact meant was that David was to become the actual jackass, and that he would be the actual one mating with the females!!!
David ran back to the door, although a little clumsily - his body seemed larger and he felt unsteady on his feet - and shouted through the small window, "Let me out of heeeraaaaw!" David froze and put his hands - or what was looking to be forming hooves - to his mouth. Even his voice was changing now! Not only that, his face felt as if it was pushing outward.
His inspection of his face was interrupted by an abrupt pain in his feet as his shoes fought against the growth. David stumbled to the ground and tugged at his shoes, managing to pull one off. Though as he pulled at the other one with his growing hooves a quick rip at the end of the shoe and stretch of his foot exposed a shiny new hoof attached to the end of his rapidly lengthening foot.
David turned over and got on his hands and knees, his growing mass strecthing his clothing to the limit. He arched his back and let out a loud, "Aarrhhheeeeahaaww!" as the seat of his shorts blew out, revealing a furred donkey tail on the end of a quickly ballooning donkey rear.
The change made David feel very dizzy as his head lengthened and his muzzle pushed out. He tried to speak again, but all that came out was a loud, "heeHaarrrwwww!!!!!". He shook hid head, as if to shake off the change, his now long donkey ears flopped back and forth. His shirt ripped down the front and back, falling to the ground. The thick dark fur on his head ran down his neck and upper back in a rough mane.
David stumbled and tried to stand up again, knowing that he had to get out of that room somehow, but he couldn't get onto his back feet. He reared up and tottered uneasily on his back hooves, but then fell back forward again, his front hooves hitting the stall's dirt floor with a dull thud. He walked slowly to the door and tried to think how to knock it down...
It was then that he noticed something in the air.. somehow he knew that thick scent... it was that jenny.. he couldn't remember her name. She smelled like she was in heat. David stared at her rear, the tail upturned, swaying slowly. Her rear hooves spread out and firm in the ground... ready to take his advances.. her vagina moist and ready, the pheromones pumping out...
'Got to... get ..out of here...' David thought in his rapildy regressing mind. He turned his rear to the door and in a sharp burst of animal power clenced his leg muscles and gave the door a quick kick with both his hooves.
The sound of splintering... David kicked again, and again, and again.... Finally, and amazingly the door burst at the hinges and fell to the ground. He turned to face the door...
But before he ran from the room he paused... this jenny wanted him, and he wanted her... his cock throbbed with his rapid heartbeat, precum oozing from the tip. Maybe... maybe he could just be with her for a quick moment... and then run... what harm could it do??
David could hear someone in the stable corridor running to the room - Henry no doubt, coming to make sure David completes the deed...
David then made his decision...