You can go half and half alfalfa/ Bermuda. One pound natural glo and a cup of flax, and a vitamin/mineral supplement or a ration balancer. BOSS is high in omega-6's, cause inflammation. Flax instead is nicely balanced.
I personally feed ration balancer, flax and a mixed hay, free choice, in slowfeeder nets. Chubby horse is steadily losing weight, the perfect one is still perfect, is gaining muscle now and the new skinny guy is rounding out nicely.
I put oathay and orchard/ timothy in the nets and feed the alfalfa in a tub on the ground.
Works like a charm.