This section is from the book "The Stable Book: Being A Treatise On The Management Of Horses", by John Stewart. Also available from Amazon: The Stable Book.
Peas are seldom used without beans, with which they are mixed in large or small quantities. They may be given without either beans or other grain, but much care is necessary to inure the horse to them. Peas seem to be very indigestible, more so than beans, and perhaps as much so as wheat; but when given very sparingly at first, they may be used with perfect safety. It is often said that peas swell so much in the stomach as to burst it. This is an error. Peas do absorb much water, and swell more perhaps than beans, but they never swell so much as to burst the stomach, for the horse can not or will not eat such a large quantity. When the stomach is burst, it is from fermentation, not from swelling of the peas. All kinds of food will produce the same result when the horse is permitted to gorge himself, or when he is fed in full measure upon food that he has not been accustomed to; but peas seem to be rather more apt to ferment than some other kinds of grain.
Peas should be sound, and a year old. They weigh, on an average, sixty-four pounds per bushel. Pea-meal is sometimes given in the same way, and for the same purposes as that of the bean. Some prefer it for diabetes, and in a few places it is given in the water for baiting on the road.
Vetch Seed has been employed for feeding horses, but I have learned nothing of the result.
 
Continue to: