Cows have four stomachs and rechew their food for hours for a reason. Leafy greens are not proper food. (Plus, they're full of toxins, both from pesticides and from the plants trying to kill anything that eats them, and tasting as horrible as possible to dissuade animals from eating them.)

The only edible parts of the plant are fruits, which are intended for animals to eat them so that they'll spread the seeds.