Feeding Standards. 239 



these determinations on the horse are not true to an equal extent 

 in the case of ruminants. In the latter the fiber is softened in the 

 paunch and its digestion has begun before it reaches the intestines. 



Net available energy then, is the available energy minus the 

 energy of digestion and preparation of the food for use. This 

 internal work furnishes heat, and provided it is not in excess 

 of the heat requirement of the animal, should not be regarded 

 as waste. The waste of heat has begun when that produced by 

 the work of digestion exceeds the animal requirement. But if it 

 is produced in the digestive tract and not in the tissues of the 

 animal, it cannot appear as useful work. 



We learn from this that it is not the total chemical energy in 

 a feeding stuff which measures its value to the body, but that 

 which remains after deducting the energy losses in the unburned 

 material of the excreta, the energy expended in digesting the real 

 fuel materials from the food, and in addition, the energy used in 

 transforming them into substances which the body can use or 

 store up. This gives us what Kellner calls the productive value 

 of feeds, and is identical in meaning with the term net available 

 energy of feeds. 



Productive value of feeds. From elaborate experiments with 

 the respiration chamber and mature oxen Kellner has determined 

 the productive value of certain feeds. For this purpose he chose 

 rather lean oxen, giving them a fixed moderate ration which re- 

 sulted in a small increase in weight. He then added to the ration 

 the feed to be experimented with, and determined the amount of 

 increase produced. This was not done by weighing the animal, 

 but by determining the amount of nitrogen and carbon retained 

 by the animal. The protein tissue stored, was calculated from the 

 nitrogen retained and the fat from the carbon left after deducting 

 the carbon required to build the increase in protein. Kellner 's 

 results are shown in the following table. 



The available energy of these feeds had already been deter- 

 mined and is given in the first column. In the second column 

 appears the percentage of loss in the process of digestion and 



