ENERGY 503 



the digestion coefficient. Digestion coefficients are usually determined 

 for crude protein, crude fiber (cellulose), nitrogen-free extract 

 (starches and sugars), and ether extract (fats). Before a digestion trial 

 can be conducted, it is necessary that the diet be fed in constant 

 amounts to the experimental subject for a preliminary period long 

 enough to ensure that the daily fecal output is representative of the 

 daily food intake. Feces are collected for a predetermined experi- 

 mental period in which records are kept of both food consumed and 

 nutrients excreted in the feces. 

 Table 21-4 displays the results of a typical digestion trial. Note 



TABLE 21-4. Total Digestible Nutrients in 100 Pounds 

 of a Steer Ration 



* The ether extract is multiphed by the factor 2.25 {%) to place all the nu- 

 trients on the same caloric basis, thus adjusting for the high yield of energy 

 from fats. 



that the digestibility of the material in the ether-extract fraction is 

 below the figure taken on page 499 as the digestive efficiency of fats 

 in human beings. Part of this difference may be correlated with spe- 

 cies, but most of it is probably due to inclusion of steroids and other 

 complex lipides not digested. In a similar way the digestion coefficient 

 of protein also appears low because indigestible nitrogen compounds 

 like the porphyrins are included since crude protein is based on the 

 determination of the total nitrogen. This value is then multiplied by 

 the factor 6.25 for conversion to crude protein. The nitrogen-free 

 extract is determined by extracting the feed with dilute acid and 

 alkali with a standard period of heating. Celltdose and lignin are 

 insoluble and make up the crude fiber. The soluble extracts are 

 titrated for reducing sugars and the results expressed as glucose. This 

 procedure measures sugars and the readily hydrolyzed polysaccharides 

 like starch, inulin, hemicellulose, and pentosans. All are at least 

 partly digested by ruminants and horses, but the last three are not 



