So what if farm animals don't usually make for the sexy shapeshifter (although centaurs are all the rage in the deodorant ad world.) Make Cowbody a reality. Because you're right: Methane gas is pretty hot stuff. And bulls, whoowhee. Worked as a minotaur, right?
Yo, I just wrote one with piggy shapeshifters--they weren't heroic. I'm thinking Turkey Warrior next. Not sure how the characteristics will shift with the h/h into human form. Maybe they can encounter danger every time there's a heavy storm. (even though it's a myth that turkeys are so stupid they can drown whilst looking up during a rainstorm, it's a GOOD myth. One I'd stick with)