87:16 When giving hay to animals on Shabbos, one may not put it in a sieve in order to remove the chaff. However, if one doesn't have the intention to sift the hay, one may use a sieve to carry it to the animal's trough. (The fact that some chaff sifts out on its own is not a problem - OC 324:1.)
87:17 One who gives bran to animals or birds on Shabbos is not permitted to add water to it (because of the prohibition against kneading). If he put water into it before Shabbos, he is not allowed to stir it on Shabbos. He may, however, pour it from one container to another in order to mix it.