You keep your eyes closed, you'd just had the strangest dream. You had started to change into a horse but had blacked out halfway through.
You flick your ear to shoo away a fly. Your ear feels strange, your face feels strange too. Your whole body feels differrent, your arms feel strong but stiff and your face feels long.
You open your eyes, and are startled. You can barely see in front of you, like your eyes are too far apart. You rise to your feet quickly, not realizing how different it feels.
Before you can realize what has happened you catch a scent, a delicious, sweet, amazing scent. You move on all fours in search of the source.
It's coming from a horse, a mare in a stall at the end of the stable. She's beautiful, you've never been a very good judge of horses but you somehow know she's beautiful. She turns her head, flares her nostrils, and presents herself to you.
A part of your mind realizes what has happened and what you are doing but your new instincts are too strong and overpower the rational part of your mind.
You take her, your new sex organ more than filling her. As your semen rushes inside of her you feel powerful, alive. You are a stunning stallion and feel ready to fuck.