Steve had always loved horses. Hell, they were the only animal he did love. So imagine his joy when he scrolled down and found "Equine" listed on the webpage. He pressed it without thinking and threw off his clothes.
The changes didn't take long to kick in. First, his skin began to change color, from pale to tan and brown, as fine horsehair started to spread over his body. More hair, thicker in volume, began to grow as well, forming a mane down his back. His legs became bent stumps, the feet and toes black hooves. A big furry tail came out above his ass, the hair dark and shiny. His neck grew out, his face became a muzzle with flat teeth and a long nose, his eyes moved to the sides of his head, and his head poked up like little stubs.
Excited, Steve immediately dropped to all fours, and found that, with his joints reconfigured, he could run like a horse. All he needed was a saddle, a rider, and a bit in his mouth, and he would ready to ride like a wind.
But now it was time for the final change. Steve had been expected this; the old expression "hung like a horse" running through his mind. As he watched excitedly, his tiny pecker began to grow until it was as long as his arm. His balls expanded until he needed both hands to hold them, and a thick foreskin spread up until half his penis was covered.
Steve wanted to go out, find a hot mare, and make some foals. But first, he needed to find that rider. And some riding gear.