"Really, I signed on for being a volunteer to a drug test, and find myself as the primary test subject in a scientific experiment. An experiment what will cause my whole bodily change to becoming an animal, and worse dooming me to living my life as if born a horse. You address me as if I should find my physical doom a personal delight, me a stud horse, and mating mares seven days of every week.
I will admit my discovering this giant new maleness does fill my mind with sensual desires, but none for a woman, rather for burying it deep inside the winking cunt of a mare. Why and or how, as I slept I dreamed of such a beastly endeavor, waking with morning wood!
Yes, I liked horses and appreciated their grace when running, but never, no never did I wish to become as then an animal. You speak of my future self as if it should be for me to consider it as a personal delight; well it ain't!
This all angers me, I want to stop what you started, but I do not know how!"
The doctor chuckled, as he said, "A certain truth, as once begun, the process cannot be reversed or stopped mid-stream. Besides, just look at what is now a part of you, what could you do with that, as it is too big to fit/slip inside a woman. Know this, that lusts and emotions tend to spur rushed waves of physical changing, as look at your hands, the skin color is much darker. Indeed, your skin is changing, becoming that of an equine, as too, you body hair will soon gain a equine pelt.
Realize this, as it was not me or my choice to cause you to change and become a working horse, I just work here at the foundation as a member of the experiment laboratory. If you were to ask me, I would admit to my being jealous of you and your present situation; maybe after witnessing your fuller transforming I might request to be the ninth test subject for the equine serum.
As yes, their were eight others who came to try the equine serum transfer experiment, two died, four became anthropic horses, three being mares and one became as a male Mule. Two completed the full process and were changed, becoming as horses. One of the two shall be your first sexual conquest, she will like that, I am sure. As why or how the process tried on a female tends to change their sense of desire for sex to nymphomaniac levels. The other changeling, became a Percheron stallion, and as best we can surmise, family heritage interacts with the process, causing a directing of the process to select the final species of an individual.
What is this, you are crying. Did my explaining of what is to come as such a worry?
Well, forget your worrying, think only of your future new self and the ways in which you can find pleasures from becoming a stud horse.
The process takes about two to three months. I shall check back with you each week during the processing, measuring your changes, the growth, your conveying to me your increased sensual lusts; like today, showing me your masculine flag."
"You really think I should be enjoying this..., well I had other plans, and those plans did not include my becoming a stud horse for your enjoyment!" As with that said my sense of emotion was at a high level, and the doctor just smiled at me.