PRINCIPLES OF STOCK FEEDING 



57 



of the digestible matter in the hay in 

 mastication, digestion and assimilation. 

 When corn meal was fed about 20 per 

 cent of the digestible nutrients were so 

 used. In the case of horses Zuntz found 

 that 48 per cent of the digestible nutri- 

 ents of the hay and 19.7 per cent of the 

 oats fed were used up in the mastication 

 and digestion of these foods. 



The difference between the amount of 

 energy which a food contains and the 

 amount required to masticate, digest 

 and absorb it is spoken of as the "net 

 energy" of the food. Zuntz states that 

 in general the coarse foods have about 

 20 per cent less "net energy" value than 

 the grains. 



It is plain that the feeding value of 

 any material should be reckoned in terms 



Fig. 37 — STEER WITH APPARATUS USED 

 IX DIGESTION EXPERIMENTS BY ARMSBY 



of "net energy" rather than in terms of 

 total digestible nutrients; for, while 

 some feeds like the hay may show a com- 

 paratively large proportion of digestible 

 nutrients, the energy required to chew 

 and digest such food may be so great 

 as to leave but little of the original en- 

 ergy of the food remaining for produc- 

 tive purposes. Feeding standards should 

 therefore be based on the "net energy" 

 value of food rather than on the total 

 digestible nutrients. Unfortunately the 

 "net energy" value of American feed- 

 ing stuffs has not yet been worked 

 out, and so we continue to make our 

 calculations on the basis of the total 

 digestible nutrients in each feed. It is 

 probable that the next step in the scien- 



tific feeding of animals will be along the 

 line of the determination of the "net 

 energy" of our feeding stuffs. 



In the animal body a ll the nutrients 

 of the food, i. e., the digestible protein, 

 the digestible carbohydrates and the di- 

 gestible fat may serve as sources of en- 

 ergy and heat. If the daily food supply 

 is sufficient to furnish all the energy the 

 body requires this is the source first 

 drawn upon. If the food supply is not 

 sufficient the fat which may be stored 

 in the body is drawn upon, and finally 

 if this source is not sufficient, the pro- 

 tein of the body itself is drawn upon. 



In all rations usually fed to farm ani- 

 mals there is 4 to 10 times as much car- 

 bohydrates and fat as protein. Much 

 of the protein fed is used in tissue 

 building and repair and in the produc- 

 tion of milk, eggs, etc. Hence much the 

 larger part of the energy of the body is 

 derived from the carbohydrates and fat. 

 Of these two constituents the fat we have 

 seen is about 2.25 times as valuable as 

 the carbohydrates. But usually there is 

 15 to 20 times as much carbohydrates 

 in a normal ration as of fat. The chief 

 source of energy and ability to do work, 

 then, is the carbohydrates. 



PRODUCTION OF MILK, EGGS, ETC 



The average of more than 5000 analy- 

 ses of samples of cow's milk show the 

 following percentage composition: 



Total solids Ash Proteid 



12.9 .7 3.2 



Fats Sugar Water 



3-9 5.1 87.1 



The milk of other farm animals con- 

 tains the same constituents as cow's 

 milk, but in little different proportions. 

 Milk does not exist in feeding stuffs 

 ready formed, but must be manufac- 

 tured by the animal. This is done by 

 special glands in the udder. Animals giv- 

 ing milk must have enough food to sup- 

 ply not only their normal wants but 

 enough in addition to supply the re- 

 quirements of milk production. 



The only source of the protein in 

 milk is the protein of the food. Should 

 this source not be sufficient the animal 

 draws on its own body for the supply. 

 The protein of the food may possibly 

 serve as a source of milk fat. It is not 

 definitely known whether it is so used 

 or not. Eecently Jordan has definitely 

 proved that milk fat is formed from the 

 carbohydrates in the ration. It is prob- 



