Pasture
A cow in the winter doesn't like to leave the barn to go to the pasture. It has to, though, because a cow's gotta eat.
ぼく
まき
None
ぼく is one of the common ways to say "I" in Japanese (which you should remember!). In this case, you're a boy... a cowboy, and you say, "ぼく will take these cows out to pasture!"