CHAPTER XVII 



THE PRODUCTION VALUES OF FEEDING STUFFS 

 i. GENERAL CONSIDERATIONS 



735. Definition. By the production values of feeding 

 stuffs, as distinguished from the relative values discussed in 

 the last chapter, is meant the actual effect produced by a unit 

 weight of the substance in maintaining an animal or in sup- 

 porting the processes of growth and fattening or of milk or work 

 production. That such production values will also express 

 relative values scarcely needs mention. 



Even at their best, comparisons based on the " digestible 

 nutrients," such as have been in vogue for many years and 

 have become familiar to all students of the subject, can show 

 only the relative and not the absolute values of feeding stuffs. 

 It is true that to the extent to which it may be assumed that 

 the digestible nutrients as determined by analyses and digestion 

 experiments actually consist of proteins, carbohydrates and 

 fats, their amount may furnish a useful clue to the nutritive 

 value of the material consumed. Even then, however, it affords 

 no quantitative measure of the results to be expected, while in 

 the case of most feeding stuffs, as appeared in Chapters II and 

 III, the actual nature of the digested material has been but very 

 incompletely investigated. Neither the chemistry of feeding 

 stuffs nor the behavior of their various constituents in metab- 

 olism is sufficiently well known to serve as the basis for any 

 trustworthy estimate of their actual nutritive effect. The lat- 

 ter can be determined only by a direct trial with the animal, 

 and during the past two decades considerable progress has been 

 made in this direction. 



736. Determination of production values. By definition 

 the production value is the effect produced upon the animal by 

 a unit of the feed under consideration. The general methods 



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