36 THE ECONOMICS OF FEEDING HORSES 



in one food the protein may be in a form easily digested 

 and assimilated, and of the total protein contained in 

 the food and taken in by the mouth a very high per- 

 centage is taken up into the animal economy and made 

 use of. It may be that in the same food the fats and 

 carbo-hydrates are much less digestible, and that of 

 the total present in the food a large proportion is wasted 

 and passed out with the excreta, having added nothing 

 to the animal economy in the way of nutrition or 

 energy. Thus it is necessary to find the percentage 

 of each nutritive constituent digested for every separate 

 food, and for the particular species of animal (horse, 

 ox, sheep, etc.) in question. The digestibility of the 

 nutritive principles of the common feeding-stuffs has 

 been worked out experimentally, as detailed in an earlier 

 chapter (Chapter III.), and it is only necessary to 

 emphasize the necessity of considering this factor in 

 deciding the true nutritive value of any food. 



Even after considering the digestibility of the proxi- 

 mate principles of a food, it is found that a comparison 

 between very dissimilar foods cannot well be drawn, 

 for it frequently happens that the digestible constituents 

 of one food are more readily assimilated and utilised 

 in the body than those of another food. This availability 

 of the digestible parts of a food largely depends on the 

 amount and kind of the crude fibre present in the food, 

 and the necessary correction may be made by deducting 



1 from the figure representing the comparative heat 

 value of that food, for every 3 per cent, (or in the case 

 of the coarse fodders, such as hay and straw, for every 



2 per cent.) of crude fibre present in it.* 



■^ This point will be made clearer for practical purposes by study- 

 ing an example, such as the calculation on p. 40. 



