Originally posted by Wolfaz:

Is there a way to tell that a max number of tamed animals in my pen was reached? Or do I have to keep an eye on them and see if there's any piggys or cubs born after feeding? Will they always eat if they can't breed anymore?

If I count squares for example, let's say 4 walls by 7 walls, so 28 squares, is there a breeding limit per square perhaps?

In addition to the info on the wiki, you can circumvent the restriction by building a breeding pair pen high up enough to let it breed almost endlessly as long as they have food. Check youtube as there are a couple of different build designs.