Don’t give them straw, there are not enough nutrients in that. What kind of hay are you feeding them? Timothy hay is very good for them, so is or hard grass hay. You can also try oat hay (not straw). Give them some choices and see what they like best. Of course make sure the hay is nice and green and free of dust and mold. Brown or pale hay has not much nutrition left in it. Ask for good horse hay.
Are they eating their fresh greens with enthusiasm?
Are they eating their fresh greens with enthusiasm?