For working horses, it is necessary that the food consist of a mixture of different kinds; for though health may be maintained on hay or grass alone, yet whenever exertion exceeds that of mere exercise, more nutriment is required to compensate for the waste, and if hay or grass only is allowed, such a quantity of these must be consumed as will cause great inconvenience to the animal by the distension they create, while a long time is needed for their mastication and digestion. Therefore grain must be given to supplement the hay, and this in proportion to the amount of work exacted; but even a mixture of grain, when this has to be given, is very advantageous, from an economical and dietetic point of view. Thus it is found that oats, and beans or peas, and maize and oats, are more beneficial than either of these grains given singly; and a variation in their relative proportion, at intervals, is also strongly recommended. So it is that in the diet scale of large studs we often find two or three kinds of grain in the ration, in addition to the hay and straw, roots and grass.
With regard to mixture of food, the object should be to furnish what is deficient in one kind of grain by another grain which contains it in large proportions.