No. 6. DEPARTMENT OF AGRICULTURE. 379 



gotten out of the food by the body, it is customary to calculate it in- 

 directly. The total food value is ascertained of the food as it 

 is taken into the body. From this is subtracted the value of the 

 undigested parts of the food and the difference is taken to represent 

 the amount of food value the body has obtained from the food. 

 From this must next be subtracted the amount of food value that 

 has been thrown off as gas, and the remainder is the net food value 

 of the ration. 



Thus, to take a concrete example: If a hundred pounds of whole 

 corn is fed a steer, the animal will digest on the average about 

 78.8 pounds. Of this amount 4.3 pounds will be fat that has a food 

 value per pound two and one-fourth times as great as the rest of 

 the material. These 74.5 pounds of digestible protein and carbohy- 

 drates plus the 4.3 pounds digestible fat are the equivalent of 84,2 

 pounds of starch in food value. 



But during digestion in the paunch this 100 pounds of corn has 

 given oiT a quantity of marsh gas that contains food value equivalent 

 to a little more than ten per cent, of its value, or 8.7 pounds digestible 

 juaterial. Deducting this from the 84.2 pounds, leaves 75.5 pounds 

 digestible material that is actually at the disposal of the animal for 

 heat, muscular energy and renewal of waste tissue. 



In the particular case of the corn, it is probable that in ordinary 

 weather there is but little more heat produced b}' the various opera- 

 tions of the body in the mastication and digestion of the corn than 

 is needed to keep uj) the necessary bodily temperature, and hence the 

 whole of the food value of the corn would be used without loss, and 

 the figures given above 75.5 pound® represents the real value for 

 maintenance of the corn. Even if this value is somewhat high, 

 owing to some waste heat, it is still true that the food value of other 

 similar grains if figured in the same way, would show similar errors 

 and in nearly the same degree. 



When, however, a comparison is made between grain and coarse 

 fodder, the results are not so reliable. If 100 pounds of timothy hay 

 are fed to a ruminant, 51.6 pounds will be digested, equivalent to 

 53.3 pounds of starch. The corresponding loss from the marsh gas 

 formed during digestion will be 11.4 per cent., or Gl.l pounds, leaving 

 47.2 pound.s as the net food value of the 100 pounds of hay. 



Is it correct to compare this with the 75.5 pounds already given as 

 the value of 100 pound's of corn? The only thing that can interfere 

 with the correctness of the comparison is a difference in the amount 

 of waste left. In masticating a pound of corn there are 26 units of 

 heat set free, while in masticating a pound of timothy hay 348 units 

 of heat are produced. If the heat from the corn was just enough for 

 Jhe needs of the body then there must be a large amount of waste 

 heat from the hay. Therefore, we can say that if the 75.5 pounds of 



