MEASURING THE USEFULNESS OF FEEDS 53 



thus preparing grain will therefore depend upon the kind of grain and 

 the class of animals to which it is to be fed. Detailed conclusions on 

 this question are presented in Chapter XVI (423) and in the respective 

 chapters of Part III. 



Contrary to much popular opinion, there is neither an increase in 

 digestibility nor any other saving thru cooking most feeds for stock. 

 (425, 922) In fact, cooking usually lowers the digestibility of the 

 crude protein of feeding stuffs. The only apparent exception to this 

 conclusion, is that for swine, potatoes, field beans, and velvet beans are 

 considerably improved by cooking. 



A comparison of the digestion coefficients for various kinds of silage 

 with those for the green forages from which the silage was made shows 

 that ensiling tends to decrease rather than increase the digestibility. 

 The exceedingly favorable results from silage feeding are therefore due 

 to the palatability of the silage, its beneficial effect on the health of the 

 animals, and the fact that less feed is wasted than with dry fodder. 



Neither the frequency of feeding, the time of watering, nor the amount 

 of water drunk appears to influence digestibility. Moderate exercise 

 tends to increase digestibility, but excessive work lowers it. 



The flow of saliva and the other digestive juices is checked by fright. 

 On the other hand, kind treatment and palatability of food should 

 favorably influence digestion. Under skillful care animals show remark- 

 able relish for their food, and it is reasonable to conclude that better 

 digestion ensues, tho no confirmatory data can be given. 



84. Influence of proportion of the several nutrients. The addition of 

 a large quantity of easily digested carbohydrates, such as sugar and 

 starch, to a ration containing much roughage may reduce the digest- 

 ibility of its crude protein, fiber, and nitrogen-free extract. 



Such depression of digestibility occurs with ruminants when less 

 than 1 part of digestible crude protein is present to every 8 parts of 

 digestible non-nitrogenous nutrients (carbohydrates plus fat X 2.25). 

 With swine the nutritive ratio may be wider before the digestibility is 

 affected. An explanation offered for such depression of digestibility is 

 that when a large proportion of soluble or easily digested carbohydrates 

 is fed, the bacteria in the digestive tract which normally decompose 

 cellulose to secure food then attack instead the more readily available 

 sugars or starch. (40) Not only is the digestibility of the cellulose, or 

 fiber, consequently lowered, but also that of the crude protein and 

 nitrogen-free extract, for the unattacked cellulose cell walls protect the 

 proteins and carbohydrates contained therein from the action .of the 

 digestive juices. This depression does not occur when nitrogenous feeds, 

 such as oil meal, are added along with the starch or sugar, thus preserv- 

 ing the balance between protein and non-nitrogenous nutrients. It is 

 assumed that this is due to a stimulation of the bacteria by the addition 

 of more protein, so that, invigorated, they attack the fiber of the food 

 again. 



