REAL NUTRITIVE VALUE OF FOODSTUFFS 39 



where N, F, and C.-H.,and D.F. = the''respective amounts 

 of protein, fat, carbo-hydrate, and fibres digested from 

 100 parts of the food.* 



Thus the nitrogenous ratio is a statement of the 

 amount of digestible proteid matter compared with the 

 amount of carbo-hydrate (including digestible fibre) and 

 fat taken together, but since these two have different 

 values in the production of heat and work, they must first 

 be reduced to the same terms — i.e., the fat must be stated 

 in terms of its equivalent of carbo-hydrate. To do this, 

 the amount of digestible fat is multiplied by the factor 2*3.t 

 For the purposes of hard town work — say a trapper in 

 London, or a dray-horse working at a trot — the optimum 

 nitrogenous ratio is found to be 1 : 5*5, or 1 : 6. 



The fatty ratio is much less important, and is simply 

 a statement of the amount of digestible fat compared 

 with digestible protein of the food. It is of some advan- 

 tage that this should be within the limits 1 : 2 to 1 : 3*5 

 in a ration for a horse at work. 



And now we are in a position to ascertain the real 

 value of any particular food. Taking 100 lbs. of the 

 food, its composition is determined by chemical analysis, 

 and the amounts of the contained protein, fats, carbo- 

 hydrates, and crude fibre are written down. Next the per- 

 centage of each of these constituents digested by the horse 

 is found from the tables, and the net amount digested 

 calculated out. Lastly, the amount of fat digested is 

 multiplied by the factor 2*3, and then by the addition of 

 the digested protein, carbo-hydrate, crude fibre, and fat 



* For the " nitrogenous ratio " of a mixture of foods comprising 

 a ration see p. 57. 



t It is, of course, obvious that these ratios are only useful when 

 reckoned on the digestible part of the foodstuff, since the un- 

 digested part is of no value to the animal. 



