ANIMAL NUTRITION DISCUSSION AT DUNDEE 435 



According to Kellner's measurements, this is rarely less than 

 95 per cent, in the case of easily digested foodstuffs but may be 

 as low as 30 per cent, in the case of tough, fibrous material, such 

 as wheatstraw. Such "percentage availabilities" of a large 

 range of feeding stuffs have been tabulated by Kellner. In the 

 case of the more fibrous foods, however, he prefers to base his 

 correction of the theoretical starch equivalent upon the pro- 

 portion of crude fibre in the food, since it is this proportion that 

 largely determines the labour required for mastication and 

 digestion of the food. 



A further difficulty in the computation of starch-equivalents 

 arises from the uncertainty as to the value which should be 

 attached to the non-protein nitrogenous ingredients of foods. 

 Kellner treated them as valueless for productive purposes but 

 this procedure perhaps hardly does full justice to these " amides." 



It remains to be seen how this method will stand the test of 

 application in practice. Its validity can only be thoroughly 

 tested by the records of experiments, conducted upon a relatively 

 large scale, in which the exact consumption of digestible pro- 

 tein, fat, carbohydrate and fibre is recorded. Such experiments 

 have, as yet, been carried out but rarely in this country. A 

 very large number of carefully conducted feeding trials have 

 been carried out but in hardly a single case has any determina- 

 tion of digestibility been made and in the great majority of 

 cases information is lacking with regard to the composition of 

 the roots, hay, straw or other home-grown foods consumed by 

 the animals. Without this information, however, it is im- 

 possible to make any stringent test of the validity of the starch- 

 equivalent as a measure of nutritive value. All we can do is to 

 make a rough test by assuming for the home-grown foodstuffs — 

 of all foodstuffs the most variable in composition — an average 

 composition and digestibility, together with similar assumptions 

 with regard to the digestibility of any other foods of known 

 composition included in the ration. 



It is not to be wondered at that the starch-equivalent 

 method has not survived with complete success every such 

 rough test that has been applied to it. Little weight can be 

 attached, however, to the results of such imperfect tests based 

 upon the results of one or two feeding trials. Of greater in- 

 terest is the comparison of the relative productive values of 

 foodstuffs as shown by their starch equivalents, with the 



