While you see a lot of information out there on what McDonald's burgers are made of, most of those stories are rumors that get started because people just plain can't stand the idea of big corporations, and want to believe that any corporation will do what they need to to raise profits. In fact, according to snopes.com
"While it's a fascinating tale, there's nothing to it: McDonald's hamburger patties in the U.S. are made with 100% USDA-inspected beef. They are cooked and prepared with salt, pepper and nothing else; no preservatives — no fillers.
Read more at
http://www.snopes.com/business/market/allbeef.asp#yziHvpB1TRcFkyBq.99"
There are no fillers in McDonald's hamburger. It may contain pink slime (which is just treated beef), and a higher fat content than you'd prefer, it is in fact beef.