Here are some things that are facts: 1. Haiwan in the area depend on ponies (places like the Everfree Forest is an exception and is considered as unnatural to ponies). 2. Sweet epal, apple Acres seems like a normal farm comparable to our farms (crops, livestock, etc.) 3. Ponies are vegetarians, confirmed sejak Pinkie Pie in "You Got to Share" song.
So under those three facts, we can say that if pigs exist outside of places like the Everfree Forest and lives near ponies, they depend on ponies to survive. They would be taken care sejak ponies like applejack (because they can be livestock in real life farms) atau sejak Fluttershy. Since ponies are strictly vegetarians, they must use pigs for other uses.
Possible pig uses: 1. To find truffles (truffles are fungi, not meat) 2. Pigs are used to eat Makanan that ponies find unsuitable for consumption. They can make good trash cleaners. 3. Pigs could be used for fertilizing crops via...dung lol. 4. They can be used for showcasing. applejack has some interests in competitions such as biggest apple. So, prettiest pig? Possible other stuff...
They might not even have a use. Ponies could just take care of pigs just because it needs a home.