I would like to cite Professor Stephen Jay Gould, upon whose work I base this this base.

Ponies keep carnivorous pets, but are herbivores. They probably do not want to kill creatures capable of thinking and feeling. In other words, the ponies would want to feed very dumb animals to their pets. ¿How would ponies figure out which critters are stupid enough to feed to their pets? ¡Science!:

Looking at vertebrates (chordates with skulls and vertebrae), one notices that brain-mass increases by the ⅔rds power of body-mass. That is nice and all, but ¿how small-brained for its body-mass does an animal have to be for being worthy of Carnivore-Chow? One notices that brains are almost always more massive than spinal chords. ¿What is the exception? ¡Some fishes!:

Fishes with brains less massive than their spinal chords probably do not have complex mental lives. It is probably okay to kill these fishes for feeding carnivorous pets.

Unfortunately, for animals without spinal chords, this line of reasoning is useless.

Caution:
Some fishes are brainy; so now, one needs to precede with extreme cation.

We have seem FlutterShy feed fishes to her pets and the father of Rarity fishing. It seems that ponies have no moral objections to killing fishes. It would not surprise me if ponies have an whole fishing industry.

¡Science helps feed Opalescence, Winona, Owlowiscious, et cetera!

3669578 But why do they have pigs then? They don't keep them as pets. They breed them. What is the purpose behind that? I can only think of one.

3669631

This is just speculation about the purpose of pigs, so take it with a grain of salt:

The ponies could use pigs as a rapid means to turn food-waste into fertilizer. In S02E05 “Sisterhooves Social”, we see that the Family Apple feed damaged apples to the pigs. Pigs also can find truffles.

3669878 Yes, that could work.

3669578 What do you mean by "brainy fishes"? I took Ichthyology in college and I don't see how that classifies a type of fish.

3671169

Brainy fishes is not a phylogenetic term but a purely descriptive term. For our purposes, a brainy fish is a fish with a brain as massive or more massive than its spinal chord. As an example, a Miss Pinkamena Diane Pie would not want to kill a Manta Ray or ElephantFishes for feeding Gummy because these fishes have brains more massive than their spinal chords. Notice that Manta Rays are in the class Chondrichthyes while ElephantFishes are in the class Actinopterygii. A fish is a brainy fish if its brain is at least as massive as its spinal chord. Phylogenetically, brainy fishes crop up sporadically all over the infraphylum Gnathostomata, but the majority of jawed fishes have brains less massive than their spinal chords.

3671246 So what, do you really think Pinkie (or Fluttershy for that matter) sit around measuring fish brains? Fish are fish in the MLP world. Unless we have an entire episode of an underwater adventure and there are talking fish--then we would have a discussion.

3671355

I can imagine ponies determining whether it is ethical to kill animals for feeding their pets by killing animals, extracting their brains & spinal chords, and measuring their masses. If the spinal chord is more massive than the brain, they feed the animal to their carnivorous pets. If the brain is at least as massive as the spinal chord, they give the body, brain, and spinal chord to Doctor Frankenstein who reassembles the animal and then reanimates it.

3669878
They can also be used to turn some field into pasture. Just look how it looks after some pigs went through: