376 VETERINARY PHYSIOLOGY 



indicated. They illustrate three different methods used to 

 compare the values of different feeding stuffs. 



(1) The Wolff-Lehmann standards were first published by 

 Wolff in 1864, and were the basis of further work done on 

 the subject. They were modified later by Lehmann. The 

 requirements are stated in terms of lbs. of total dry sub- 

 stances, and of digestible protein, carbohydrate, and fat. 

 The nutritive ratio is also given. 



These standards were originally based on the conception 

 that protein was especially valuable for fat formation and for 

 work. The protein requirement therefore as stated is too 

 high. The part of the food-stuff taken as digestible is the 

 apparent digestible portion (p. 3 6 4). This is not a certain indi- 

 cation of its energy value to the animal. From this should 

 be deducted — (1) the loss of energy in fermentation, and 

 (2) the energy of certain non-nitrogenous substances that 

 appear in variable amounts in the urine of herbivora). 

 These substances are chiefly derived from the fodders, and 

 consequently the energy value of fodders as calculated from 

 the apparent digestibility is less than the real energy value. 

 The productive value of a food therefore is not always the 

 same as the value calculated from the digestible nutrients. 



(2) Kellner's Standards. — In these it is recognised that 

 the apparent digestibility of a food is not a reliable indication 

 of its productive value. Foods are therefore compared 

 according to their fat-forming value. Starch is taken as the 

 standard, and it is estimated by Kellner that the fat-forming 

 power of the digestible nutrients of the food bear the 

 following relationship to starch : — 



1 part protein , . ~ 0*94 parts starch equivalent. 



1 part fat, in coarse fodders, 



chaff, and roots . . =1'91 „ 



1 part fat, in grain . =2*12 „ 



1 part fat, in oil seeds . =2-41 „ ,, 



1 part nitrogen-free extract 



and crude fibre , . =1*00 ,, „ 



The value of a food is determined by multiplying the 



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