AD&DPlanescapeKings of the Wild accessory: The creatures of the Beastlands (a heavenly realm, also known as the Happy Hunting Grounds) hunt and eat each other—c'est la vie. Because the possibility of being devoured by Owl is just part of what it means to be Mouse. Moreover, to kill an animal without subsequently eating it is "the ultimate insult" to the whole species (and possibly all other species under the same Animal Lord's rule). "Predators Are Mean" was invoked once, and this ultimately was the stupid mortals' fault. Initially at least the Animal Lords themselves (who can assume humanoid form) were exempt from the menu, but times changed. On the other hand, the Mouse Lord, being the ultimate "sneaky rodent", is so good at hiding and escaping that only the Owl Lord can hunt him down.
Unknown if it's been retconned since or not, but the Beastlands had a sort of "Valhalla-esque" vibe—anything that died there (whether eaten or not) would revive the next day. Thus the Mouse Lord being eaten by the Owl Lord isn't so much utterly destroyed as inconvenienced for a few hours, maybe a day. Well, eaten alive then inconvenienced for a few hours.
Subverted in the Ravenloft setting's domain of the Wildlands, where all the Talking Animals have a mean streak regardless of ecological niche.
Also AD&D Example but not involving animals, it's quite common for Always Chaotic Evil Races to eat anything not their race, like Giants, Orcs or Goblins. On a more horrifying level, Illithids even breed and enslave Anything That Moves as tasty snacks and workforce. Also in one novel it's stated that humans make bad slaves for drow, because they are way too prone to rebelliousness, but they are quite useful for trade connections or if you run low on other food...
The Lunar Exalted in Exalted have the innate ability to assume the form of animals. They acquire new forms by killing an animal of the appropriate species (presumably after hunting it down themselves) and drinking its fresh blood in a very literal case of "you are what you eat". And given the right charm, they can use this trick with humans as well...
Averted in the "furry RPG" Ironclaw, where only mammals and birds are anthropomorphic, leaving reptiles (lizards, dinosaurs, dragons) as the beasts of burden and livestock.
Explicitly addressed in the Wonderland No More Supplement for Savage Worlds - There is a difference between Animals (with a capital letter, such as Cats or Owls) which are intelligent and animals (with a small initial, cats and owls) that aren't. While it is perfectly OK to eat the latter, eating one of the former is a serious social faux pas - even though some Animals cannot help just smelling too tasty (as per a disadvantage).