34 



MAINTENANCE EATIONS OF FARM ANIMALS. 



ble energy in fat. 1 On this basis we may compute from Rubner's 

 final averages (p. 28) that to maintain the dog experimented on, 

 that is, to make good the loss of 54 calories of energy per kilogram, 

 it would haA T e been necessary to supply per kilogram the following 

 amounts of metabolizable energy in the materials named : 



Calories. 



In meat protein 79. 3 



In gelatin 78. 1 



In fat 61.9 



In cane sugar 57. 3 



These figures afford a simple illustration of the fact that the amount 

 of metabolizable energy required for maintenance is variable, being 

 greater as its availability is less. The maintenance requirement of 

 the dog was 54 calories of available energy. The maintenance ration 

 needed to supply this varied according to the material which served 

 as the carrier of the energy. 



The same relations hold good for farm animals, although the fact 

 that we can not well observe their fasting katabolism directly makes 

 the computation a trifle more complicated. As an example, we may 

 take the experiment on timothy hay already cited on page 20. The 

 addition of 2.1 kilograms of timothy hay, equivalent to 3.575 therms 

 of metabolizable energy, to the basal ration reduced the loss of energy 

 from the body of the animal by 2.020 therms. Evidently, then, to 

 have reduced it by 2.377 therms, that is, to zero, would have required 

 2 377 



the addition of 2.1 X ' ft9n = 2.471 kilograms of the hay, equivalent 



to 4.207 therms of metabolizable energy. The total maintenance ration 

 of this particular feeding stuff, then, would have been the basal 

 ration plus this amount, or 5,670 kilograms of the hay, equivalent to 

 9.894 therms of metabolizable energy. 



The same result may also be obtained by the use of the percentage 

 availability as computed, viz, 56.5 per cent. The heavier ration 

 failed to maintain the animal by 0.357 therms, that is, it lacked this 

 amount of available energy. To supply this requirement would evi- 

 dently demand 0.357^-0.565=0.632 therms of metabolizable energy, 

 which added to the 9.262 therms already contained in the ration 

 gives a total as above of 9.894 therms. The same computation can, 

 of course, be made from the lighter ration with the same result. 



From the data given it is likewise possible to compute what the loss 

 by the body would have been had it been practicable to withdraw all 

 feed. The basal ration contained 5.687 therms of metabolizable 

 energy, of which 56.5 per cent was available ; that is, the basal ration 

 was capable of preventing the loss of 5.687X0.565=3.213 therms from 



1 On the assumption, of course, that the effect is a linear function of the amount of 

 food. 



