MEASURING THE USEFULNESS OF FEEDS 47 



and rice can not be ground they should be cooked or soaked. Musty 

 hay and corn fodder are made more palatable and safe by steaming. 

 In winter it is often advantageous to give vi^arm feed to pigs, but this is 

 entirely different from cooking the feed. 



Curing and ensiling forage. — If green forage is cured without 

 waste and in a manner to prevent fermentation, the mere drying does 

 not lower its digestibility. Ordinarily, however, in curing forage 

 much of the finer and more nutritious parts is wasted, and dews, rain, 

 and fermentations effect changes which lower digestibility. The 

 large amount of work done in masticating dry forage and passing it 

 thru the alimentary tract is another reason why green forage may 

 give better results and hence appear more digestible than dry forage. 

 The long storage of fodders, even under favorable conditions, 

 decreases both their digestibility and palatability. 



Ensiling green forage tends to decrease the digestibility. The 

 exceedingly favorable results from silage feeding must therefore be 

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

 of the animals, and to the fact that less feed is wasted than when 

 dry fodder is used. 



Influence of amount of feed eaten on digestibility. — Animals tend 

 to digest their food somewhat more completely when given a main- 

 tenance ration than when on full feed. This may be due to the more 

 rapid movement of the food thru the digestive tract or to a less com- 

 plete absorption of the digested nutrients when present in large 

 amount. Under normal conditions, in feeding farm animals for the 

 production of meat, milk, or work, other economic factors, which will 

 be treated in later chapters, more than offset the slightly better utili- 

 zation of feed when a scant ration is fed. 



Influence of proportion of the different 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 

 digestibility 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 this lessened 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 and starch. 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 



