122 THE CHEMISTRY OF CATTLE FEEDING 



any substance that is only partially oxidised gives out only a 

 part of its heat. A more or less considerable part of the food 

 the indigestible matter always remains unoxidised and is 

 excreted as faeces. The protein and carbohydrates of the 

 digested portion are not completely oxidised in the animal's 

 body. The residual products derived from the former are 

 excreted in the urine, and those derived from the latter pass 

 out as gases. 



In order to estimate the physiological heat value of the 

 food, />. how much of the potential energy is converted into 

 the kinetic form of heat in the animal's body, the fuel values of 

 the residues the dung, urine, and gases must be deducted 

 from the total fuel value of the food. In the case under con- 

 sideration the figures are 



Food. Dung. Urine. Gases. 



(Kt.) (Kt.) (Kt.) (Kt.) (Kt.)' 



3-65 - (1-61 + -035 + 0-173) = * '83 



It will be noticed that though the total potential energy of 

 the food is 3-65 kt. per lb., only 1*83 kt. about half the 

 total amount is available to the animal. 



The fuel values of the residues cannot, as a rule, be 

 determined directly, nor is it necessary, as they can be easily 

 calculated as follows : 



(1) The composition of the dung from 100 Ibs. of hay 

 can be found from the composition of the food and the co- 

 efficients of digestibility ; and the T.F.V. can be calculated 

 as before. 



TOTAL FUEL VALUE OF THE DUNG. 



Constituents indigestible. Per cent. Factor. Fuel value. ^Kt'T' 



Oil- . ...... i'5 x 8-5 = 1275 . 



"Albuminoids" (proteins) 6'o X 5'8 = 34-80 I . ._ 



Carbohydrates and\ l6 95 



Crude fibre } 2 7 X 4*2 = 113-40) 



(2) It is shown (p. 172) that 0-343 parts of urea are 

 formed from each part of protein digested. The fuel value of 

 urea is 2-542 kt. per lb. The fuel value of the urea from 

 i lb. of protein is, therefore, [2-542 X 0*343 =] 0-872 kt. ; 



