Funny, when I added dogs to "chlorophyll in lawn grass"...got this link 3 little Pitties.
This kind of explains, but gives you couple things to try...you could also try spirulina or chlorella - chlorophyll oxygenates the blood.
Why Do Dogs Eat Grass?
He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion. - Unknown