Cant think of any. Traditionally they were fed because they were cheap. "Oats contain the lowest concentration of digestable energy of the common cereals".However quite often horses are allergic to them and it produces hyperactivity so they are ideal for racehorses but they need a specific balancer. Some horses, feeding oats doesnt making any difference but others it can produce stroppy behaviour. When I started riding there were only straights no cubes. If you fed bruised barley there were similar results but we always used to boil barley to make it more digestable. Oats are £3.25 for a bag locally. Most race horses still seem to be fed oats and bran but this diet is unbalanced.The phrase "Had his oats" refers to the hyperactivity effect.