87:12 One may untie a bundle of hay that’s not tied with a permanent knot – i.e., a double knot – and place it before his animals. One may cut up a hard gourd (though not into very small pieces – Mishnah Brurah 324:15) to place before an animal so long as it was picked before Shabbos. If the gourd is soft enough for the animal to eat it “as is,” the owner may not cut it up on Shabbos.
87:13 One may place his animal on grass that is still attached to the earth so that it can graze. It’s not considered work for the animal to uproot the grass – it’s the animal’s form of pleasure! (For an animal to refrain from this activity would not be “rest,” it would be suffering! – MB 324:33.) Grass that was cut by a non-Jew on Shabbos is considered muktzeh, so one may not bring his animal there to eat unless it has no other food. If the animal has nothing else to eat, the owner may use this grass in order to prevent the needless suffering of animals (tzaar baalei chaim). Similarly, if the animal has nothing to drink, one may ask a non-Jew to bring it water from a well in a carmelis (the quasi-public domain).