ESSAYS 319 



THE NUTRITIVE VALUE OP FEEDING-STUFFS (J. Alan 

 Murray, University College, Reading). 



It was formerly believed that the nutritive value of a feeding-stuff was determined 

 entirely by its composition and digestibility. The sum of the percentages of 

 digestible protein, carbohydrates and fat multiplied by 2 - 3 was called the "total 

 digestible nutrients," and the ratio of the sum of the last two to the first is still 

 called the " nutritive ratio." This view obtained until it was shown by Kellner 

 that the digestible nutrients of hay and straw did not produce so much body fat as 

 equal amounts of the same digestible nutrients in a pure state or in various cakes 

 and meals. To account for this he advanced the hypothesis that more energy is 

 expended on the mastication and digestion of coarse fodders, and he attributed 

 this to the presence of the hard lignified fibre they contain. The fact that the 

 productive value of wheat straw is increased appreciably when the straw is finely 

 ground, and to a much greater extent when it is reduced to pulp, before being 

 consumed, was regarded as confirmatory evidence. 



He therefore proposed to deduct from the total digestible nutrients a sum 

 equal to about three-fifths (0*58) of the percentage of crude fibre. His experi- 

 ments showed that this adjustment was satisfactory for hay and straw, but for 

 grasses and green fodders the factor (0*58) had to be reduced by C05 for each 

 2 per cent, of fibre below 16 per cent, as follows 1 : 



Crude fibre per cent. 16 

 Factor . . . '58 



A certain correction was found to be necessary also in the case of cakes and 

 meals, but it could not be made in this way. He therefore determined the rela- 

 tive productive value of the nutrients in these foods, and expressed the results by 

 means of a number called the " value " of the food. This may be concisely 

 expressed by the formula — 



v — \oof\F, 



where/ is the amount of body fat produced by the digested nutrients in any 

 quantity of the feeding-stuff, F is the amount produced by equal weights of the 

 same nutrients (digested) in a pure state, and v is the value number. 



The data obtained in the course of these investigations enabled him to revise 

 the coefficients of equivalence for fat-production of the several nutrients, and he 

 attempted to express the nutritive values of the various kinds of feeding-stuff in 

 terms of an equivalent amount of starch. If we accept his view 2 that, without 

 serious error, 1 part of fat may be reckoned equal to 2 - 2 parts of starch in all cases, 

 this is concisely expressed by the formula — 



S.E = (2'2F +C+ o"94/ > ) x t//ioo 



where F, C, and P are the percentages of digestible fat, carbohydrates (including 

 fibre) and protein respectively, v is the value number, and S . E is the starch 

 equivalent of 100 parts of the feeding-stuff. 

 In the case of hays and straws : 



S.E = {rzF + C + o-94P)-o-s8p, 



where p is the percentage of total crude fibre. For green fodders the calculation 

 is made in the same way, but the factor 0*58 is varied as described above. 



1 Scientific Feeding of Animals, p. 356. 

 8 Ibid., p. 357. 



