My horses have been on straight grass hay all their lives. When we lived in TX they were on a Coastal hay and now in AZ they are on a Bermuda grass hay. I only buy good quality hay and have been accused of having a pregnant gelding a time of two. I have just now started feeding my 25year old EQ. Senior since he does not have much tooth left and can't get all the nutrients out of his hay. I am a firm believer in a horse must have roughage ( hay of some sort) it is how they are designed and it benefits their health.