FAT PRODUCTION 197 



The value number for hay is 58, and the true 

 starch equivalent therefore 41-86 x 58 -^ 100= 24. 

 This figure means that 100 Ib. of average meadow 

 hay may be expected to produce as much fat as 

 would be produced by 24 Ib. of starch. Kellner's 

 value numbers vary from 100 for very easily di- 

 gested foods to 30 for such foods as straw which 

 are digested with difficulty. The need for them 

 arises from the fact that in the case of easily 

 digested foods practically the whole of the di- 

 gestible nutrients are available for fat production, 

 whilst in the case of such foods as straw 70 per 

 cent, of the energy of the nutrients is used up in 

 the processes of mastication and digestion and only 

 30 per cent, is left over for fat production. 



It is interesting to note that the value number 

 for articles like sawdust is a minus quantity, which 

 means that when such articles were added to a 

 maintenance diet the energy required for their mas- 

 tication and digestion exceeded the energy of the 

 digestible nutrients they contain. These were in 

 fact digested at the expense of the energy of the 

 rest of the food and the animal to which they 

 were given decreased in weight instead of storing 

 fat. 



Starch equivalents determined by Kellner's 

 method are intended to measure the relative value 

 of different foods for fat production. They should 

 therefore be called production starch equivalents, 

 and they may be used as an index of value for 



