I visited Cornell University, Ithica, NY last year and personally saw the fistulated cow. Just like this one in the picture, the cow was eating and didnt really care about the hole in its side, or the many people watching her stomach contents mulching inside. It was a cool thing to see, and I was relieved that it did not cause her pain or discomfort- otherwise they would have heard from me!
What does the fistulation do? -- I think one of its purposes is to have an easy access to the stomach contents. If other cows get some sort of illness, this cow's stomach bacteria can help the other cows get better (I think thats how it goes).
WANT TO KNOW ALL ABOUT A FISTULATED COW?
Go Here: Fistulated Cows at UC Davis