Animal cheese

I have often wondered whether cheese could be made from non-standard cheese-producing animals.

I've eaten cow cheese, goat cheese and sheep cheese, and I've heard of yak cheese. Why is there no pig cheese? Pigs are mammals. They produce milk. Why can't that milk be turned into cheese? I'm sure it would become a yuppie delicacy in no time. Or how about horse cheese? I can already see the menu - "Arugula salad with raspberry-caper vinaigrette, olive bread croutons and horse cheese," or "Pig-cheese asparagus ravioli with a champagne cream sauce."

So why not?