As with anything new gradual, make sure they have had hay first and you can put them out on small section at a time over short period of time gradually increasing time grazing and space depending on how much grazing there is they will soon munch it down but if it is a large area cutting it may be helpful, section off a bit for hay ? It's the new lush growth that can be danger of bloat but feeding hay / straw will balance the lush stuff.