320 



SCIENCE PROGRESS 



Kellner's hypothesis that the difference in productive value of the digestible 

 nutrients in various kinds of food is attributable to expenditure of energy in masti- 

 cation and digestion of the lignified fibre is not easily reconciled with the necessity 

 for this difference in the method of calculation or with certain other facts. On his 

 own showing, 1 the "value" of linseed meal, which contains 9 per cent, of crude 

 fibre, is 96, whereas that of palmnut meal, which contains 25 per cent., is 100, and 

 that of beet molasses, which contains none, is only 87. He also showed that 

 digested pure fat does not produce its own weight of body fat, but only from 50 

 per cent, to 60 per cent, of that amount. In other words, from 40 per cent, to 

 50 per cent, of the energy of the digested fat disappears, and is, presumably, 

 expended on mastication and digestion of the substance. The same is true of 

 starch and other ingredients. These phenomena are not due to the presence of 

 fibre, and the hypothesis appears to be untenable. As a matter of fact, it is 

 erroneous. The apparent loss of energy in the digestion of wheat straw is not 

 diminished when the straw is pulped ; the increased productive value arises 

 merely from the larger amount digested. 2 



The loss of energy observed by Kellner, however, is real— whatever the cause 

 may be — and that the productive value of the nutrients is not the same in all feed- 

 ing-stuffs is a fact. When this was realised, the starch equivalent system was 

 readily accepted. There was no alternative ; and it cannot be denied that it 

 affords a more reliable indication of the nutritive (productive) value than does the 

 "total digestible nutrients." For the purpose of calculating rations, however, it is 

 of little significance unless the maintenance requirements can be stated in the 

 same terms. Kellner arrived at his conclusions in regard to this by the practical 

 method of adjusting rations to the maintenance requirements, and calculating the 

 amount of starch equivalent to the same. The mean result 3 of several experi- 

 ments was 4-f lb. per day for oxen of 1000 lb. live weight, but he recommends 61b. 

 as the standard to be used in practice. More recent investigations show that the 

 latter is nearer the truth. 



The amount of pure starch required for maintenance of ruminants cannot be 

 determined by direct experiment, because these animals cannot subsist normally 

 on such concentr'ated food. Neither can it be inferred from the normal heat- 

 emission, for that depends not only on the size and condition of the animals, but 

 also, to a large extent, on the quantity and quality of the food consumed. The 

 whole of the me tabolisable (thermic) energy of the maintenance ration is ultimately 

 given out as heat from the body, and the heat-emission of an animal consuming 

 the quantities of food equivalent to 6 lb. of starch would, therefore, be as follows : 



N.B. — A kilo pound unit (kt) of energy is the amount given out from 1000 lb. 

 of water when cooled i°C, .'. kt x 454 = Cal. Also kt per lb. = Cal. per gram = 

 Therms per kilogram. 



1 Scientific Feeding of Animals, tables pp. 360 et seq. 



2 Arm&by, /tfz/r. Agric. Resources, 191 5, p. 485. 



3 Scientific Feeding of Animals, p. 244. 



