Star slow, make homemade prune puree (or a good quality store-bought prune puree) and use about 1 oz (30 g) - about 2 tablespoons for first feeding. Wait a few hours and see if it's working, if not, try another serving, same amount. And work your way up until you see results. To avoid blowouts is best to mix prune puree with oat porridge, it will keep thing going smoothly.