We allow 1lb per day per month of age up to 5 lbs after which we keep them at 2.5 kilos per day until slaughter. We do feed masses of veg in the winter, which we reduce as the weather gets warmer. It works for us. I have always understood that with the exception of kune kunes pigs do not get any real feed value from grazing. Of course the act of ripping up the grass provides hours of fun, and loads of exercise as well as satisfying their natural needs to do so.