UTILIZATION OF FOOD 425 



with the result that the average deficit was found to be only 0.073 

 gram of fat per i gram of crude fiber fed. The deficiency was 

 no doubt due in part to the character of the nitrogen-free extract 

 of hays and straws, which, as is well known, is not composed of 

 sugars and starch, but largely of substances hard to dissolve and 

 in part of unknown nature. They are not the same as the starch 

 used by Kellner to represent the pure nutrient. 



Calculating Productive Value. Knowing the composition and 

 coefficient of digestibility, the productive value in terms of fat 

 of a given feeding-stuff may be calculated so as to be in accord 

 with the experimental work cited. The results are expressed in 

 pounds fat which may be produced by 100 pounds of feed. 



Concentrated Feeding-Stuffs. Multiply digestible proteids in 

 100 pounds fed by 0.235. Multiply digestible fat by 0.598. 

 Multiply digestible nitrogen-free extract and crude fiber, taken 

 together, by 0.25. Add the products, and multiply by the per- 

 centage of fat produced by the feeding-stuff in question as per 

 preceding table. If the feeding-stuff is not named in the table, it 

 will be necessary to use the factor for the feed most closely 

 resembling it. The result is approximately the productive 

 value in terms of fat. Chaff, rice hulls, and other by-products 

 high in crude fiber are not considered as being concentrated feed- 

 ing-stuffs. 



Roughage. Proceed as directed above, using the factor 0.526 

 for digestible ether extract in grasses, and 0.474 for all other 

 roughages, and sum up the fat values of the nutrients. Then, if 

 the roughage is not ground, multiply the total quantity of 

 crude fiber present in 100 pounds by 0.14 and subtract this quan- 

 tity from the sum. If the roughage is ground, multiply the crude 

 fiber by 0.07 and proceed as before. With green feeds contain- 

 ing 8 per cent, or less crude fiber, deduct 0.085 gram fat for each 

 gram of crude fiber; with those containing 8 to 10 per cent., 

 deduct 0.095 ; with those containing 10 to 12 per cent., deduct 

 0.108; with those containing 12 to 14 per cent, deduct 0.12; 14 

 to 16 per cent., deduct 0.135; over J 6 per cent., deduct 0.14. 

 28 



