One of the scariest scenarios I can think of is a bull getting loose on a small ship. You cannot kill it (you have centuries to wait until you can just transport straws of semen), you need it for the colony, you have to secure it again. Realistically it would probably be something simple along the lines of "Bellow, Smash, Splash".
Oddly this is something I have been wondering about – a combination of watching 'Firefly' and playing 'Serenity' (Mongoose, you would have done a far, far better job) and something that came up at a recent Folklore Association meeting. For short distances you can swim the beasts – tie their heads alongside the boat but for long voyages, such as the Icelandic settlers it must have been horrible.
Presumably you take weaned calves (smaller and more manageable) or young heifers and bulls (bigger but tougher) or pregnant cows in the hope that you will get a bull calf though I would wonder if they might abort with the stress and poor diet of the voyage.