It's tricky because they're so big, but cows are roasted on spits whole all the time. Boiled? Not so much. According to Weird Asia News, "during a Food Festival in Sheng Yang China, one company boiled a 1,500 lbs cow. It was 1.3 meters long and 2.5 meters high." The boiler itself was capable of containing three tons of water, and it took ten hours to boil the cow.
(The photos might make you squeamish, so if you're in doubt don't click through!)