We may untie bundles of grain for our animals on Shabbos, but we may not chop hay or carobs because those are edible as is. Principle: we make sure our animals can eat, so we render the inedible edible, but we don’t exert ourselves to make the food any finer than that. We may cut meat from a carcass for dogs. Why the special privilege? See Exodus 11:7, “no dog shall whet its tongue against Israel…” We may not overfeed or force-feed our animals on Shabbos since such a practice would benefit us rather than them. We may not feed a pig on Shabbos since we only feed animals whose feeding is our responsibility and Jews don’t raise pigs. We may add water to bran for the animals, but we may not do the work of mixing because it’s too similar to the prohibited labor of kneading.