I doubt any size pen would keep grass for very long but I would like them to stay relatively clean. Will share a common fence line. Combination pnels and 4 inch wooden posts every 8 ft. each will have a simple 3-sided shelter. How big if I plan to use to house 2 calves per pen overnight? Additionally where do people who allow their calves to stay with dairy mom, keep those calves as they get older in order to get first or second milking from mom? When do you wean and sell them? Thank you in advance.