If the defect (hole) in the part is small enough or the path length for the leak is long enough, it will be almost impossible for the fluids to flow through the hole (leak). The fluid properties that affect flow are pressure, temperature, and viscosity.
Though the answer seems to be correct, but when taken from that perspective, one will not keep focused on the real reason. The main reason why we shoe horses is for work, which then determines the style and the type of shoeing for the individual working horse. Various types of historical horseshoes.
Horses can do well on grass or alfalfa (or other legume) hay. Important factors to keep in mind for horse hay are the nutritional needs of the animals (mature horses will not need high protein or calcium levels unless they are mares nursing foals), and the way the hay was harvested.