If you pair a male pig and a female pig together for a certain period of time, a piglet will come out.
A pig can only pair 1 pig at most.
You can ship an already paired pig from the pigsty.
You can pair your female pig into a male pig. If you have your own male pig in the pigsty,
bring that pig to the pig plaza and then, you'll be able to pair them together.
If there's no male pigs around you, you can rent a male pig from another owner (rental fees occur)
After pairing them together, the male pig goes back to the male fence and will be able to ship them.
The female pig will be lying down near the center fence until they give birth to a piglet.
After a certain period of time, it gives birth, and the newborn piglet will be automatically moved to the pigsty. (If there's an open spot in the pigsty)
If there's no space for it, it will be standing-by inside the pig plaza as "waiting pigs".