178 The Feeding of Animals 



The productive value is stated in terms of the 

 available energy less (1) the energy devoted to the 

 work of chewing and digestion, and (2) that which is 

 appropriated to the molecular rearrangement of the di- 

 gested compounds which are transferred to the body 

 substance. 



These being the factors which diminish productive 

 value, it is easy to understand how the usefulness of a 

 nutrient is somewhat determined by its source. When 

 it is contained in a coarse fodder like straw where the 

 work of chewing and digestion is large and where, 

 because of its physical condition, the fodder is slowly 

 acted upon by the digestive fluids and is thus subject 

 for a long time to the action of micro-organisms, the 

 nutrient is less valuable than when supplied to the ani- 

 mal in grain where the work of mastication, digestion 

 and solution is a minimum. Starch, extracted straw 

 and molasses, requiring no energy for mastication and 

 but little for solution, supply digested material which 

 Kellner found to be four times as valuable for pro- 

 duction as that coming from ripe wheat straw. 



The foregoing figures do not tell us how much a 

 steer would gain daily when fed upon a certain quantity 

 of these nutrients, but they do indicate in a general 

 way what is the relative efficiency of the nutrients 

 when derived from given sources. They give us a 

 scientific explanation of the fact that coarse foods are 

 not adapted to rapid production. 



Relative imjyortance of the protein compounds. — 

 Much prominence has been given to the fact that 

 protein includes several groups of nitrogen compounds 



