what i found works well is five pens, arranged in a circle with about 6m between each pen (one long core wood log and a short one for spacing). With five pens you can get over a stack of meat off a single breeding, so its like 10 mushroom/carrot/whatever for 20+ meat (using two star boar). Once you feed simply hang out a few minutes, wandering off can cause them to stop breeding, think the game culls some actions from happening away from players for the most part, so keep it in mind.