1. The animal experimented upon to be supplied daily with a weighed quantity of food, the composition and calefacient value of which had been accurately determined. 2. The gases, vapors, and liquid and solid egesta thrown off from its body to be collected, analysed, and the calefacient[!--15--][15] value of the combustible portion of them to be determined. 3. The increase (if any) of the weight of the animal to be ascertained. 4. The difference between the amount of heat evolvable by the foods before being consumed, and that actually obtained by the combustion of the egesta into which they were ultimately converted, would be the amount actually set free and rendered available within the body. The calculations would be somewhat affected by an increase in the weight of the animal's body; but it would not be difficult to keep the weight stationary, or nearly so, and there are other ways of getting over such a difficulty. An experiment such as this would be a costly one, and could not be properly conducted unless by the aid of an apparatus similar to that employed by Pettenkofer in his experiments on respiration. This apparatus, which was made at the expense of the King of Bavaria, cost nearly £600.
Value of Manure.—It is a complication in the question of the economic feeding of the farm animals that the value of their manure must be taken into account. Of the three classes of food constituents, two—the mineral and nitrogenous—are recoverable in the animal's body and manure; the non-nitrogenous is partly recoverable in the fat. I shall take the case of a sheep, which will consume weekly per 100 lbs. of its weight, 12 lbs. of fat-formers, and 3 lbs. of flesh-formers. Twelve per cent. of the fat-formers will be retained in the increase, but the rest will be expended in keeping the animal warm, and the products of its combustion—carbonic acid and water—will be useless to the farmer. It is, therefore, desirable to diminish as much as possible the combustion of fatty matter in the animal's body; and this is effected, as I have already explained, by keeping it in a warm place. Of the flesh-forming substance only five per cent. is retained in the increase, the rest is partly consumed in carrying on the movements of the animal—partly expelled from its body unaltered, or but slightly altered, in composition. The solid excrement of the animal contains all the undigested food; but of this only the mineral and nitrogenous constituents are valuable as manure. The nitrogen of the plastic materials which are expended in maintaining the functions of the body is eliminated from the lungs, through the skin, and by the kidneys—perhaps also, but certainly only to a small extent, by the rectum.
The food consumed by an animal is disposed of in the following way:—A portion passes unchanged, or but slightly altered, through the body; another part is assimilated and subsequently disorganised and ejected; the rest is converted into the carcass of the animal at the time of its death. The undigested food and aliment which had undergone conversion into flesh and other tissues, and subsequent disorganisation, constitute the excrements, or manure, of the animal. The richer in nitrogen and phosphoric acid the food is, the more valuable will be the manure; so that the money value of a feeding stuff is not determinable merely by the amount of flesh which it makes, but also, and to a great extent, by the value of the manure into which it is ultimately converted.
Corn and oil-cakes are powerful fertilisers of the soil; but the three principles which constitute their manurial value—namely, nitrogen (ammonia), phosphoric acid, and potash—are purchasable at far lower prices in guano and other manures. Nevertheless, many farmers believe that the most economical way to produce good manure is to feed their stock with concentrated aliment, in order to greatly increase the value of their excreta. They consider that a pound's worth of oil-cake, or of corn, will produce at least a pound's worth of meat, and that the manure will be had for nothing, or, rather, will be the profit of the business. The richer food is in nitrogen and phosphoric acid, the more valuable will be the manure it yields. It follows, therefore, that if two kinds of feeding stuff produce equal amounts of meat, that the preference should be given to that which contains the more nitrogen and phosphoric acid. Mr. Lawes, who has thrown light upon this point, as well as upon so many others, has made careful estimates of the value of the manure produced from different foods. They are given in the following table:—
| TABLE Showing the estimated value of the manure obtained on the consumption of one ton of different articles of food; each supposed to be of good quality of its kind. | ||||
| Description of Food. | Estimated Money Value of the Manure from One Ton of each Food. | |||
|---|---|---|---|---|
| 1. | Decorticated cotton-seed cake | £6 | 10 | 0 |
| 2. | Rape-cake | 4 | 18 | 0 |
| 3. | Linseed-cake | 4 | 12 | 0 |
| 4. | Malt-dust | 4 | 5 | 0 |
| 5. | Lentils | 3 | 17 | 0 |
| 6. | Linseed | 3 | 13 | 0 |
| 7. | Tares | 3 | 13 | 6 |
| 8. | Beans | 3 | 13 | 6 |
| 9. | Peas | 3 | 2 | 6 |
| 10. | Locust beans | 1 | 2 | (?)6 |
| 11. | Oats | 1 | 14 | 6 |
| 12. | Wheat | 1 | 13 | 0 |
| 13. | Indian corn | 1 | 11 | 6 |
| 14. | Malt | 1 | 11 | 6 |
| 15. | Barley | 1 | 9 | 6 |
| 16. | Clover-hay | 2 | 5 | 0 |
| 17. | Meadow-hay | 1 | 10 | 0 |
| 18. | Oat-straw | 0 | 13 | 6 |
| 19. | Wheat-straw | 0 | 12 | 6 |
| 20. | Barley-straw | 0 | 10 | 6 |
| 21. | Potatoes | 0 | 7 | 0 |
| 22. | Mangolds | 0 | 5 | 0 |
| 23. | Swedish turnips | 0 | 4 | 3 |
| 24. | Common turnips | 0 | 4 | 0 |
| 25. | Carrots | 0 | 4 | 0 |
All the saline matter contained in the food is either converted into flesh, or is recoverable in the form of manure, but a portion of its nitrogen appears to be lost by respiration and perspiration. Reiset states that 100 parts of the nitrogen of food given to sheep upon which he experimented, were disposed of as follows:—
| Recovered in the excreta | 58·3 |
| Recovered in the meat, tallow, and skin | 13·7 |
| Lost in respiration | 28·0 |
| ——— | |
| 100·00 |
Haughton's experiments, performed upon men, gave results which proved that no portion of the nitrogen of their food was lost by perspiration or by respiration. Barral, on the contrary, asserts that nitrogen is given off from the bodies of both man and the inferior animals. Boussingault states that horses, sheep, and pigs exhale nitrogen. A cow, giving milk, on which he had experimented, lost 15 per cent. of the nitrogen of its food by perspiration. The amount of nitrogen which Reiset states that sheep exhale is exceedingly great, and it is difficult to reconcile his results with those obtained by Voit, Bischoff, Regnault, Pettenkofer, and Haughton. Of course, men and sheep are widely different animals; but still it is unlikely that all the nitrogen of the food of man should be recoverable in his egesta, whilst nearly a third of the nitrogen of the food of the sheep should be dissipated as gas. I think further experiments are necessary before this point can be regarded as settled; and it is probable that it will yet be found that all, or nearly all, of the nitrogen of the food of animals is recoverable in their egesta.
Regarding, then, an animal as a mechanism by which meat is to be "manufactured," five economic points in relation to it demand the feeder's attention: these are—the first cost of the mechanism, the expense of maintaining the mechanism in working order, the price of the raw materials intended for conversion into meat, the value of the meat, and the value of the manure. In proportion to the attention given to these points, will be the feeder's profits; but they are, to some extent, affected by the climatic, geographic, and other conditions under which the farm is placed.