If you purchase and install the pasture, there will be a "pasture" billboard
inside the "pigsty".
If you touch the billboard, the screen will jump to the pasture.
If you want to bring your pig to the pasture, drag your pig to the right side of the screen.
It should bring your pig to the pasture.
Make sure to keep your pig in the pasture until the pig status shows "done"
If you want to bring your pig back to the pigsty, drag your pig to the left side of the screen.