I'm no expert, but I wonder about this being an Australian Cattle Dog. Brindle (the stripes) is not a listed color for them. (Simon and Schuster's Guide to Dogs. It really looks like a German Shepherd to me, or a Belgian Turveren, but it is hard to tell from the picture.. Unfortunately, my dog book, and many others usually only have pictures of adults. The pupply could look totally different than and adult...
It is a really cute puppy, though.. I would definitely find out what it was before I would commit. Australian Cattle Dogs have "an atavistic habit of biting at the heels of cows (and people.) per my book..