Prairie Oyster Harvest (Side Mission)
After completing Testy Festy, talk to Casey again for the second part of the questline. It'll see you wantonly mutilating a number of cows, so maybe give this one a miss if that's not your thing.
If you're in, head to the Davenport farm west of town.
Shoot the lock off the cattle pen here to set your targets free.
You now have to kill three cows in three different ways. One, mid-coitus.
The next, by shredding it with the mulcher (the blue tractory thing with the decidedly unhygienic and inhumane spinning blades- there's one north of the pen).
The last you need to burn alive- a molotov will do if you don't have a flamethrower.
Loot the carcasses, then follow your marker to Casey and the Fest, in the field south of the Purpletop Telecom Tower.
Talk to Casey to advance to the last part of the mission.
The quest ends with a minigame. Look down and take a shot, then shoot all the balloons within 40 seconds. This isn't too hard- your vision will be swimming a bit, but just aim for the center of each bunch.
Getting them all doesn't seem to win you any additional prizes, you just blackout and wake up with the pigs, and mission completion. And a special outfit.