36 FEEDS AND FEEDING, ABRIDGED 



Digestion coefficients. — The average percentage of each nutrient 

 digested in a feeding stuff is termed the digestion coefficient, or 

 coefficient of digcstihility, for that nutrient in the feed. In Appendix 

 Table II are given the digestion coefficients for some of the leading 

 American feeds, selected from the extensive table in the unabridged 

 edition of ' ' Feeds and Feeding. ' ' This table shows that feeds which 

 contain little fiber, such as corn and wheat, are highly digestible, 

 because the cell walls are thin and easily penetrated by the digestive 

 juices. The higher the fiber content of feeds, the thicker and more 

 resistant are the cell walls, and consequently the less digestible are the 

 feeds, as a rule. Thus, oats and wheat bran are less digestible than 

 corn or wheat, and the roughages, such as hay and straw, have still 

 lower digestion coefficients. In general, the nitrogen-free extract of 

 feeds is slightly more digestible than the crude protein or fat, and 

 much more digestible than the fiber.^ 



Digestible nutrients in feeding stuffs. — To find the digestible 

 nutrients in any feeding stuff the total amount of each nutrient in 

 100 lbs. of it is multiplied by the digestion coefficient for that nutrient. 

 For example, 100 lbs. of dent corn contains 10.1 lbs. of crude protein 

 (See Appendix Table I), of which 74 per ct. is digestible, as shown in 

 Appendix Table II. Accordingly, there are 10.1 X 0.74 or 7.5 lbs. of 

 digestible protein in 100 lbs. of dent corn. In this manner the authors 

 have computed the data in Appendix Table III, which show the 

 digestible nutrients in the important American feeding stuffs. (This 

 table is condensed from the exhaustive and complete table in the 

 unabridged edition of "Feeds and Feeding.") For purposes of illus- 

 tration, the following examples are presented on the next page. 



In Appendix Tables I and II the fiber and nitrogen-free extract are 

 given in separate columns, for, tho of the same chemical composition, 

 these components often differ widely in digestibility. In preparing 

 tables of digestible nutrients, the digestible fiber and digestible nitro- 

 gen-free extract are determined separately and the results combined 



1 In digestion trials it is commonly assumed tliat all matter appearing in tlie 

 feces represents the part of the food which is actually indigestible. This is only 

 approximately correct, for the feces always contain some waste from the body 

 itself, such as bile residues, matter coming from the walls of the alimentary 

 canal, and unabsorbed digestive juices. Also, as we have seen in the preceding 

 chapter, thru the action of bacteria in tlie paunch and large intestine, some of 

 the nutrients, especially the fiber, are broken down into gas, which has no nutri- 

 tive value. Yet this is usually included in the amount considered to be diges- 

 tible. Furthermore, in digestion studies the ether extract, or so-called fat, is 

 extracted by ether, which dissolves not only the true fat, bvit also the chloro- 

 phyll, wax, bile residues, and other substances which are not true fat. Due to 

 this, and because the fats in feeding stuffs are usually in relatively small amount, 

 errors are liable to occur in finding their digestibility. 



