amount of heat produced by such an animal, whether determined 

 directly or by calculation, shows how much energy it is drawing 

 from the materials of its body, while the amount of nitrogen con- 

 tained in the urine shows how much protein is being broken down. 



With cattle, owing to their voluminous and complicated di- 

 gestive organs and the considerable amount of feed which the latter 

 still contain even after long fasting, this method is not practicable. As 

 regards the protein requirement, all that is possible is to determine 

 by trial, in the manner illustrated on subsequent pages, the amount 

 of digestible protein in the feed which suffices to prevent a loss of 

 protein from the body. It is possible, however, by an indirect 

 method to determine the energy requirement of fasting cattle. 



Indirect determination of energy requirement. 

 A steer consumed per day in two successive periods 7.05 pounds 

 and 11.68 pounds of timothy hay, neither ration being sufficient to 

 maintain the animal. The amount of heat produced daily in each 

 period, as measured by means of the respiration calorimeter, was: 



Hay eaten Heat produced 

 Ibs. Therms 1 



Period IV n.68 9.70 



Period III 7.05 8.06 



Difference 4.63 1.64 



The addition of 4.63 pounds of hay in Period IV increased the 

 heat production of the steer by 1.64 Therms, or at the rate of 0.35 

 Therms for each pound of hay. This is entirely in accord with the 

 well established fact that an increase in the amount of feed con- 

 sumed tends to cause an increase in the heat production of an ani- 

 mal. If, now, instead of adding more hay to the ration of Period 

 III, hay had been withdrawn from it, it may be assumed that the 

 heat production would have decreased at the same rate as it ac- 

 tually increased. Tf, then, it had been possible to withdraw all the 

 feed, the heat production would have been diminished by 0.35 X 

 7.05 2.47 Therms; that is, the heat production of the fasting ani- 

 mal would have been 8.06 2.47 - = 5.50 Therms. By thus com- 

 paring two periods upon different amounts of feed, it is possible 

 to get indirect! v the amount of energ-v required to carry on the 

 necessary vital processes, i. e., the maintenance requirement as de- 

 nned in the previous paragraph. 



1 A therm, equal to 1000 large calories, is the amount of hout required to 

 raise the temperature of 1000 kilograms (2204 pounds) of water 1 C C. 



(8) 



