Originally posted by Zarkow:

Do you have pigs in the hut above too or...?

yes, thats the point of breeder. Piglets drop down and are far enough to bypass breeding limit at one location. In a few ingame days i can have 50 or more boars in the pit. They breed at insane rate, but you must be near the breeder. If you move too far, they will stop breeding until you get back.