It's Surry! First time she's been shown with her dapples and fetlocks, just an all around amazing piece of art by TheBraveLittle over on FA.

Original can be found here: http://www.furaffinity.net/view/12783108/
If you like it, go tell the artist; I'm sure he'd love to hear from you! ^^ Also watch him (If you're on FA, of course), his art is totally awesome. and worthy of much praise and attention.