I have heard that what the pig has been fed can affect the taste of the meat. This too happened to me with Waitrose pork (chops) a few years ago - the meat looked and smelt fine raw but once cooked it was inedible.
The one and only time I've had diorrhea (sp?) was in Bulgaria on our honeymoon 21 years ago. I ate something that tasted like shite (food was scarce and generally horrible), and then literally 10 minutes later it came out the other end, hot and smelling the same as it smelt when I ate it.