Ooh! Ooh! I think I know this one too!
I'm pretty sure you're thinking of an artist named fetishdrawer. Unfortunately it looks like they deactivated their DA account. I did a quick DA search and a very few pictures were re-posted by someone else (
http://chainedknee.deviantart.com/ar...F24180576&qo=3) but sadly not the horse tf, which was probably my favourite of their stuff.