T24 THE CHEMISTRY OF CATTLE FEEDING 



stationary condition, i.e. not growing, fattening, working, or 

 producing milk, the heat or kinetic energy resulting from 

 oxidation of the food is dissipated in several ways, viz. (i) in 

 warming the ingesta and respired air ; (2) by evaporation of 

 water from the skin and lungs ; (3) by radiation from the skin. 



The amount of heat required to warm the ingesta (the 

 food and water consumed) can be investigated from known 

 data. 



By definition (p. 119), i kt. is the amount of heat required 

 to raise the temperature of 1000 Ibs. of water i C; so o'ooi 

 kt. is the amount required to raise the temperature of i Ib. of 

 water i C. Therefore 



H = o-ooiM(T 1 T 2 ) 



where H is the amount of heat (kt.) required, M is the mass (in 

 pounds) of water consumed, Tj is the temperature of the animal's 

 body, and T 2 that of the water. Practically the same formula 

 may be used for the dry matter of the food ; but it must be 

 multiplied by the specific heat (0-5) of the dry matter. 



The temperature of the animal's body is practically con- 

 stant. For farm animals it is about 100 to 104 F. say 

 40 C. The temperature of the ingesta may be anything from 

 less than o C. up to 20 C. or more. 



Example. Suppose an ox to consume 50 Ibs. of roots at 

 a temperature of 10 C., and that they contain 90 per cent, of 

 water and 10 per cent, of dry matter, then 



H = o'ooi X 45 X (40 10) = i'35 kt. for the water. 



H = 0*001 X 5 X 0*5(40 i o) = 0-075 . dry matter. 



i.e. 1*425 kt. is required to warm the whole of this ingesta to 

 the temperature of the body. 



If the available energy of the roots is about 0-29 kt. per 

 Ib., 4*9 Ibs. would be used merely to warm the food to the 

 temperature of the animal's body. Of this quantity, 4*66 Ibs. 

 would be required for the water and only 0-24 Ib. for the dry 

 matter. The loss of heat due to warming the ingesta, apart 

 from water, is not, therefore, of much account. 



The amount of heat lost by evaporation of water may be 



