Pigpen

The Pigpen is a storage Building which was released on August 26th 2010. It was slowly released to all users during the day as a gift. It requires 8 Wooden Boards, 8 Nails, and 8 Bricks to build.

You can have a maximum of 1 Pigpen, and it can be harvested every 23 hours which is half the 46 hour harvest cycle time for the individual pigs. On harvest, you have a 15% chance of gaining an item (possibly a consumable like the Horse Stable).

You can see the animated pop-up you may receive here.

Truffle Hunting
On September 3rd, 2010, Stage 2 of the pigpen was released: Truffle Hunting.

First, you need to create Slop from Bushels in your Stall. Any 1 Bushel = 1 Slop.

When you feed slop to a pig, they hunt on Neighbor farms for Truffles.

1 Slop will feed 1 Pig. You can only feed 20 pigs per day and once you feed a pig, they're tired and will sleep for 2 days.

Hours after being released, there was a game-wide rollback. After which the Truffle Hunting was gone (disabled). It is assumed it was due to massive bugs related to finding truffles on a 'null' farm. It is unknown whether these 'null' farms are just a bug, or previous users who have left farmville and blocked the application, but when you found a truffle on a null farm, you were unable to post to a user wall to eventually get the truffle back. Approximately 50% of all truffle finds were on 'null' farms, leading to users wasting their slop, and cooldown on their pigs.

Pigs
Different types of animals that can be placed into a pigpen: