[Daemon]

I am looking for a story that I happened across some time ago and seem to have lost. I can't remember the name only a few details of the actions that take place:

1. a man happens across a female goat and is compelled to have sex with her.
2. during #1, a male goat mounts the man.
3. the man transforms gender wise and the male goat transforms into a satyr/man-goat thing.
4. the man goat/satyr proceeds to mate the woman, transforming her into a nanny goat.

Any advice on the story title and location would be appreciated.