378 VETERINARY PHYSIOLOGY 



measuring what is essentially the energy of a food leads to 

 confusion. The logical as well as the simplest unit for this 

 is the Calorie. The method of calculating the starch value is 

 open to question. One gram of protein is almost certainly not 

 equal to 0-94 grams of starch for fat formation on account 

 of its specific dynamic action (p. 272). In foodstuffs rich 

 in protein the error must be considerable. Even if the 

 relative starch values be taken as accurate, the values are 

 for fat formation and are not applicable without error for 

 other purposes. 



(3) Armsby's Standard. — In these, food requirements are 

 stated in terms of pounds of digestible protein and "therms" 

 of "net energy," and the accompanying tables of food values 

 give the lbs. of protein and therms of net energy per 100 lbs. 

 of the different food-stuffs. A therm is 1000 calories. 

 " Net energy " is available energy minus the energy liberated 

 as heat in the increased metabolism due to food con- 

 sumption. It is regarded as the " productive energy value " 

 of the food. 



The following extracts illustrate the way in which the 

 food requirements and food values are stated : — 



Maintenance requirements for Cattle. 



Table of Food Values. 



