Lifting the latch Rebecca moved into the crate beside the donkey.
She fell to her knees and started to crawl under the donkey, her long ears brushing the donkeys underbelly.
With her conscious still crying out at her she lifted the soft donkey penis in her hands and started to guide it towards her mouth.
As the head approached her mouth she started to give it long licks with her tongue. Not after long she started to feel its cock stirring and started to slowly harden and lengthen. As it lengthened she opened her mouth slightly to allow it push inside.
Between Rebeccas legs was now soaked and the wetness had started to spread down from her crotch onto her thighs.
The donkeys cock was still lengthening and growing thicker causing Rebecca to open her mouth wider to accommodate it. With it's increased length she started to rock her head backwards and forwards causing it to slide in and out of her mouth.
As the pleasure increased Rebeccas body started to change further.
Her legs could no longer be contained within the dungarees. Rebeccas legs began to reshape further into the hind legs of a donkey. The muscles in her thighs started to bulge even larger and the seams of the dungarees began to split along her legs causing her thighs to burst out. Her thighs began to shorten and her legs started to force their way under her body causing her to raise up off her knees and rest on her hooves as she started to become a quadruped.
Unable to wait any longer she pushed the donkeys cock out of her mouth and unfastened the buckles of her dungarees with one hand and pushed the remains of the dungarees off her body revealing her large ass, sex and now even longer tail to the donkey above her.
She turned her body pushing her ass up towards the donkeys cock and stood expectantly waiting, resting on her hind legs and with her hands out in front of her.
Realizing the opportunity the donkey started to probe for her sex with its cock. Rebecca could feel it attempting to enter and started to urge it on.
"Come on get inside me! I need you in me hawwww!"
In a moment of sudden ecstasy Rebecca felt the donkeys cock surge forward pushing her lips apart and sliding deeper inside of her.
As it thrust in and out of her Rebecca started to let out small whinnies of pleasure. Her arms were starting to change as well now. Her upper arms started to bulge with muscle as they were changing from arms to forelegs.
"I'm changinggggggg" Rebecca moaned.
Her body started to get larger. Her back started to arc causing her shirt to split and her breasts to fall out. She started to squeeze one of her large breasts with her hand while supporting herself with the other.
Her body started to fill out more. Her back started to push up against the donkeys belly as she grew larger. Her chest barreled out absorbing her breasts into her body leaving her with a pair of pointy nipples.
The donkey continued to pummel away as Rebecca continued to grow. The donkey started to raise up onto its hind legs and hunched over her back. Her hindlegs and forelegs bulked up further to allow her to stand on her frame as she became a proper quadruped.
Her curly pubic hair started to thicken into fur and spread out from her black donkey sex to cover her body.
Rebecca looked down to see her hands started to spasm as they darkened and thickened into hooves.
Finally the last remainder of her humanity started to change.
"I want to be a donkeyyyyhawwwww" she brayed in pleasure as the donkey started to unleash its load inside of her.
Heehaw heehaw heehaw she brayed as her mouth and nose started to fuse.
Heehaw heehaw heehaw she brayed again as finally her face fully pushed out into a muzzle and left her standing there as a jennet.