The Chronivac had changed her back to normal after she'd tried being gay. Considering the risks there, getting mounted by a normal healthy bull when she was a normal healthy cow was perfectly safe. She relaxed, allowing her bovine instincts to take over.
It was really strange - Mark was aware of everything, but at first she was more a passenger in the cow's body as bovine thoughts dominated. Her sex was hot and slick, and she raised her tail and braced herself for the bull. He jumped up once, then slid off. Then he managed to leap up with a better position, and worked forward until the head of his massive bullcock pressed against her rump.
Her need was overpowering, and Mark began to slip into the bovine mindset fully. She was no longer a passenger - she and cow were the same creature, the same mind, the same...
The bull thrust in and drove deep, sending a wave of intense pleasure and fulfillment that fused the thoughts in Mark's head into a single consciousness. The cow had no thoughts other than mating, no purpose other than to be mated. And when the bull shot his seed into her, she joined him bellowing their lust and satisfaction.
They remained joined for a few more minutes, and then the male slid off and licked her sex. He remained with her the rest of the day, mounting her twice more before moving on to another cow.
Mark's need had been satisfied, and when the other bull snuffled curiously, she shooed him away with a kick of a hind hoof. The rest of the week passed quickly, though she no longer comprehended time as anything but periods of light and dark.
She was chewing cud on a pleasant warm day when the odd feelings started. Some of her sisters snuffled in her direction and began to move away nervously. Her scent was changing! More than that, her whole body seemed to be getting smaller. She was confused. She was now the size of a young calf or heifer, and her fur was falling out. A bellow of terror came out of her changing mouth as a weird yell.
There was movement by the thing that kept them in the grass place. Humans! Several males leaped the thing that kept them in the grass place and came running toward her. She wanted to run away, but discovered that her hooves were gone! She had pink wiggly things that were too soft to walk on, and her forelegs were twisted horribly.
The humans began making excited noises, and she cringed in fear.