You lay on the floor of the changing cell, looking up at the horse-girl that just entered. She looks down at you with look of concern.
Tears roll down your cheeks. Your diaper is full of two loads of horse manure, and you can feel your stomach somehow churning up a third. You try to stand but only make it to your knees. The horse-girl kneels down next to you, putting one hand on your shoulder and the other on your soft, bulging diaper. You can feel your bowels tighten and you buttocks strain against the torrent of shit that is filling up in you.
"It's Ok honey, this is what it's for. It's natural to have accidents in a diaper. You don't have to be ashamed. Just let it go, like a real horse."
You are too distracted by the fact that you haven't stopped pooping in this diaper since you put it on to realize that the front of your diaper has been growing as well. Your cock begins to stir again, and even though it's still stiff, it seems like it is expanding...
Then again huge load of horse shit explodes into the diaper, pushing it out so far that it almost touches the floor.
"Good boy." Says the horse girl. "Now, we'd better get you changed before we send you off with your new item."
"What the hell is this thing!?" You cry, now sobbing in confusion and humiliation.
"It's a horse diaper, of course! But it wouldn't be much good if it never got used now, would it? Once you commit to wear it, your body will start making enough manure to make it necessary."
"When does it stop?" you ask.