THE DAIRY.

New Zealand Mail, Issue 1314, 6 May 1897, Page 5

THE DAIRY.

THE SCIENTIFIC SIDE OF CATTLE FEEDING. HOW THEY USE THE DIFFERENT ELEMENTS IN THEIR FOOD. Digestion is the changing of feeds in the stomach and intestines into soluble and diffusible substances, that can be taken up by the blood. The process, briefly stated, is as follows : The food is chewed in the mouth, and thoroughly moistened by the saliva. The moistening of the feed thus enabling it to be easily swallowed, is the principal value of the saliva. The slightlychewed feed passes to the large first stomach, or paunch, and then into the smaller or second division. The food, thus softened, is returned from the second stomach to the mouth and more thoroughly masticated, and then passes to the third stomach. This third stomach has numerous folds, between which the food is pressed, and the soluble portions directly resorbed. It then passes into the fourth stomach, where ordinary process of digestion begins in the same manner as in animals having a simple stomach. The feed is here subjected to a considerable motion, and is acted on by the so-called gastric juice, the active principles of which .are pepsin and hydrochloric acid. This action of these substances changes the protein into a soluble form called peptone. Neither the fat nor the carbo-hydrates (sugar, starch, and gum) undergo any change in the stomach. Small amounts of some kind of protein are so changed in the stomach as to be taken directly into the blood. But by far the larger part of the food, now termed chyme, goes from the stomach into the intestines, to be further acted upon. The digestive fluids of the intestines are the bile or gall of the liver, the pancreatic juice of the pancreas, and the intestinal juice. The chief use of the gall is to divide the fab into very minute globules, that is, to emulsify it. The bile also aids in the resorption of the fat. The pancreatic juice contains a ferment called trypsin, which acts powerfully upon the various forms of protein, changing any that escapo the action of the pepsin of Lho stomach, into peptone, and still further converting a part of the peptone into other simpler substances. Another, no less important, ferment is the ptyalin, which converts a considerable part of

the stavch and similar carbohydrates into sugar (maltose). The pancreatic secretion also acts in the same way as does the bile of the liver upon the fat, bringing it into a very finelydivided condition. The action of the intestinal secretion is not fully undeij} stood, a small amount of ptyalin, which changes starchy matters into sugar.

In addition to the several secretions mentioned, various bacteria play a considerable part in the process of digestion in the small intestine. They decompose or break down more or less protein convert starch into sugar, and decompose the woody fibre, which hitherto has not been acted upon, into a variety of simpler substances. The food in this soluble condition is taken up by a multitude of so-called epithelial cells with which the intestines are lined, and carried with more or less change into the blood, there to serve as a source of nourishment. That portion of the feed which has not been made soluble passes on into the large intestine, and is finally excreted as solidment, which is nothing more than the undigested part of the feed. It contains one half of the nitrogen, and three-fourths of the phosphoric acid execreted by the animal daily, the rest of the elements going off in the urine, ! which also contains nearly all of the potafii excreted. After tbe protein or nitrogenous matter, carbohydrates, and fat have been made soluble and taken into the blood, they are transported to the multitude of cells, composing the body. The vital force of the cell—the cell juice of protoplasm—shatters or breaks the larger part of them into simpler substances, thus liberating heat and vital energy. This process is completed by the oxygen of the blood still further decomposing them into carbonic acid and water, which are transported to tbe lungs and exhaled. All three forms of food elements, therefore, serve as sources of heat and energy. Special Uses and Characteristics of the Protein.—This (the nitrogen-con-taining element in the food consumed) is, perhaps, a source of fat, and is tbe only source of flesh. It is also—in the form of casein or curd—a very prominent constituents of milk. Before it becomes flesh or casein it is more or less reconstructed by the cells. When protein is broken up and transformed into heat and energy, a considerable portion of its carbon and hydrogen is exhaled by the lungs as water and carbonic acid. With its characteristic element—the nitrogen—this . is not possible. The nitrogen is transformed into urea, and being of no further use is carried by the blood to the kidneys and excreted as a prominent constituent of the urine.

Experiments have proved that the more protein an animal consumes, the more will be decomposed and changed into heat j in other words, the quantity of protein consumed governs the quantity destroyed. At the same time, the more protein fed up to a certain point, the greater will be the tendency of the animal to put on flesh or produce milk. Too large an amount of protein cannot be fed, because cattle, sheep, and hogs and not able to digest and assimilate it; even if this were possible, it would not be economical, the protein being the most costly of the three food elements. The animal must have a certain amount of feed to produce heat and energy, and this can be more cheaply secured from the carbohydrates. Protein is necessary to replace the wastes of the body, to form flesh, and to enable milk-producing animals to give maximum and continuous milk yields. Special Use of the Carbohydrates. — The sugar and starch, besides being the

principal source of heafc and serve as the chief source of fat.

Special Use of the Fat:—Experiments have proved that fat yields two and one half times as much heat as the carbohydrates. Animal fat is also formed from the fat of the feed, but as a rule not directly ; i e : the fat molecule is more or lesss pulled to pieces and reconstructed. The lives of hone of our farm animals can be sustained by protein, fat, carbohydrates, or ash alone ; and yet all are absolutely necessary to sustain life and produce growth. Experiments proving the above ficts teach us that for the securing of specific ends, such as the production of flesh, fat or milk, these several groups of substances as found in our various agricultural plants should not be fed at haphazard, but rather in reasonable definite pioportions, depending upon the end sought. It is also clear that a feed is valuable as a source of nourishment only so far as its various constituents can be digested and assimilated. Thus 1901 b of good timothy liay yield nearly 501 b of nutriment that is actually digested and made use of by the cow, compared to only 351 b in an equal weight of swamp hay.—Extracted from Professor J. B. Lindsay's Essay, P>ulletin of the Massachusetts Experimental Station.