ANIMAL NUTRITION DISCUSSION AT DUNDEE 433 



in them of small quantities of an ingredient or ingredients 

 whose character has not yet been determined. Further we 

 have reason to believe that the interchange of fat and carbo- 

 hydrate is safe only so long as certain minimum amounts of 

 each are present in the ration. Lastly we may mention the 

 factor of palatability, which has been found to exercise an 

 influence, within certain limits, upon the nutritive efficiency 

 of foods consumed by farm stock. 



Further blame for the discrepancies alluded to above might 

 easily be put upon the crudity of the analytical units in terms 

 of which the composition of foods is expressed. 



Protein, carbohydrate and fibre, as commonly returned in 

 the analysis of foods, are not definite chemical individuals but 

 more or less complex groups of ingredients ; the amounts of these 

 present are arrived at, moreover, by methods which are not of a 

 high order of accuracy. In the case of "carbohydrates " indeed, 

 for want of a feasible method, no attempt at a direct determina- 

 tion is made but the amount is simply arrived at by difference. 

 Added to these shortcomings are the further crudities of the 

 estimation of digestibility. Of these only one need be mentioned 

 — the assumption that all material removed from the food during 

 its passage through the animal has been " usefully " digested. 



In the face of all these complications and difficulties, it is 

 obviously impossible to devise any system of computing food 

 values that will give more than a rough estimate. 



For the purposes of the farm, however, the rough estimate 

 will, in most cases, be sufficient and it would obviously be 

 foolish to abandon even the old method of arriving at such an 

 estimate, without further test of its value when modified in 

 accordance with the outcome of recent research. 



It will be generally agreed that, provided it be satisfactory in 

 other respects, the nutritive value of a ration will be determined 

 by the amount it contains of assimilable protein, fat and carbo- 

 hydrate. Assuming that the ration is suited in bulk and 

 character to the animal and consists of sound foodstuffs, the 

 chief "other respects " that need to be satisfied will be, so far 

 as present knowledge informs us, the character of the proteins 

 and "amides" present and the inclusion of the little-known 

 ingredients whose presence, though only in minute amount, is 

 essential for the efficient utilisation of the food in the body. 



In a simple ration, such as is often fed to pigs, there is risk 



