After the horse has been accustomed to a certain kind or mixture of food, it is not to be suddenly changed. By inattention to this, many errors prevail re garding a horse's food. It is extensively believed that boiled food, barley, carrots, and some other articles, produce purga-iion - that raw wheat is poisonous - that peas swell so much as to burst the stomach -that potatoes, and many other things, are flatulent.

The truth is, a sudden change of diet produces evils which would not occur were the change made with care. The most frequent result of a change is colic, next to that purgation, and after these come founder, surfeit, weed, constipation, and apoplexy. Some of these, perhaps the whole of them except purgation, may arise as often from the horse eating too much, as from the sudden change. But it appears quite certain that the stomach and bowels requite some little time to adapt themselves to articles upon which they have not been accustomed to act. The horse eats too mush, because the new article is more palatable than his ordinary food; and the groom often gives too much without knowing ; he gives barley and beans in the same measure that he gives oats. These articles, and wheat, are much heavier in proportion to their bulk. An equal weight of oats might not be eaten, though it were given, and the horse would suffer no evil, but if the horse is not used to beans or barley, he will eat a greater weight of those than of his oats; if an equal quantity by weight, were given, the horse would be in less danger; b ri still it is not safe suddenly to substitute one article for another.

If it were determined to use a certain portion of barley instead of oats, say an equal quantity of each, the change is not to be made in one day nor in one week At first give the barley in only one of the daily feeds, and in small quantity, so that, during the first week, one feed will consist of three parts oats, and one part barley - the other feeds will be the same as usual; in the second week, one fee 1 will be half oats and half barley; in the third week, give two of those feeds every day; in the next, three, and so on till the horses receive the allotted quantity.

One dose of physic, perhaps two, may be useful when the diet is altered; but if the horses be seasoned, and in full work, it is seldom necessary. It is most required when the food is richer and more constipating than that to which they have been used.

The Quantity of Food may be insufficient, or it may bo in excess. The consumption is influenced by the work, the weather, the horse's condition, age, temper, form, a\ d health these circumstances, especially the work, must regulate the allowance.

When the horse has to work as much and as often as he it able, his allowance of food should be unlimited.

When the work is such as to destroy the legs more than i exhausts the system, the food must be given with some re striction, unless the horse be a poor eater.

When the work is moderate, or less than moderate, a good feeder will eat too much.

When the weather is cold, horses that are much exposed to it require more food than when the weather is warm.

When the horse is in good working condition, he needs less food than while he is only getting into condition.

Young, growing horses require a little more food than those of mature age; but, as they are not fit for full work, the difference is not great.

Old horses, those that have begun to decline in vigor, require more food than the young or the matured.

Hot-tempered, irritable horses seldom feed well; but those that have good appetites require more food to keep them in condition, than others of quiet and calm disposition.

Small-bellied, narrow-chested horses require more food than those of deep and round carcass; but few of them eat enough to maintain them in condition for full work.

Lame, greasy-heeled, and harness-galled horses require an extra allowance of food to keep them in working condition.

Sickness, fevers, inflammations, all diseases which influence health so much as to throw the horse off work, demand, with few exceptions, a spare diet, which, in general, consists of bran-mashes, grass, carrots, and hay.