(...cont)
However, younger animals can be different. Earlier this year a calf of ours broke its leg. Weighing only a few stone, a plaster cast could support his weight. Being young he healed quickly, and we could take the cast off after four weeks -- and he's now almost as good as new (his leg's slightly kinked, but he doesn't limp). But then he will only be needing it for a couple of years, and he won't need to carry a rider, nor gallop much.
It might be possible to do the same with a (much more spindly) young foal, but I rather doubt it. (Incidentally our vet's bill for that simple break was probably more than the profit we'll get from the steer.)
The other thing to realise about horses is that they really enjoy working, much as a dog enjoys walks and chasing sticks or rabbits. My cob sulks if I don't take her out, and never gets so excited as when she's pulling a load up a hill or through thick mud (she's bred for draught). Even she, as a relatively staid "cold-blood", will gallop madly around the field without any encouragement from me. A racehorse, of course, is bred for racing.