Most will require grain in addition to hay. All will need grain and hay. When pasture is available, the amount of hay needed will be reduced. Feeding programs based on alfalfa hay often provide protein in excess of a horse's requirement, particularly when large amounts of alfalfa are fed to mature horses at maintenance or light work. However, there is no evidence to suggest that a moderate dietary excess of protein is detrimental to healthy, mature horses.
Protein is made up of amino acids which are composed of carbon, hydrogen, oxygen and nitrogen.
Thus it is possible that horses consuming high protein diets will drink more water and urinate more than horses consuming a lower protein diet, but there is no reason to believe that a horse's kidneys will be damaged when this occurs. Alfalfa cubes are an acceptable alternative to baled alfalfa hay. Voluntary consumption may be higher when alfalfa cubes are fed than when long hay is fed. There are two potential advantages of alfalfa cubes over baled hay. Currently, hay cubes are used more commonly in the Western U.S. than in other areas.