70 PRINCIPLES OF FEEDING FARM ANIMALS 



periments with ruminants, that the best conditions for the digestion 

 of rations fed are found when these contain about one part of diges- 

 tible protein for every eight parts of digestible non-nitrogenous 

 substances (including fat multiplied by 2.25). In the case of swine 

 a depression in the digestibility of carbohydrates will not occur until 

 starch has been added in sufficient quantities to bring the nutritive 

 ratio of the ration down to 1 : 12, and the digestibility of the crude 

 protein was not affected by a ratio of 1:9. The result of experi- 

 mental work shows that the maximum nutritive effect of a ration 

 can be obtained only when the relation between the digestible protein 

 and non-protein (the nutritive ratio) lies within certain limits that 

 may not be outside of 1 : 8 in the case of ruminants and 1 : 9 to 12 

 in the case of pigs. 



Other Components. The addition of free acids, like sulfuric 

 or lactic acid, will not influence the digestibility of a ration or of 

 its components. Since there are large amounts of free organic acids, 

 like lactic, acetic, and butyric acids, in silage, particularly of the 

 first two acids, this result is important. It is not recommended, 

 however, to give such feeds in large quantities to cows whose milk is 

 used for infant feeding, or for feeding young stock, as they have a 

 tendency to cause looseness of the bowels. 



The effect of many other materials on the digestibility of feeding 

 stuffs has been investigated, like calcium carbonate, common salt 

 (sodium chloride), and other mineral salts. In general, no influence 

 on the digestibility of feeds has been observed in experiments con- 

 ducted for the study of these problems. A moderate amount of com- 

 mon salt will improve the palatability of a feed, however, and may 

 cause an animal to eat more and thus give better returns, if this is 

 adapted to the specific purposes for which it is kept. A good dairy 

 cow, e.g., if stimulated to consume larger amounts of feed than be- 

 fore, will respond to the more liberal feeding by an increase in her 

 milk production, while a cow not bred consistently " along dairy 

 lines," with a view to securing a large milk production, will put on 

 body fat under similar conditions, and the milk yield will be likely to 

 decrease as a result. 



QUESTIONS 



1. How do steers and sheep differ in their ability to digest (a) coarse 



feeds ; ( & ) concentrates ? 



2. What is the main difference in the digestive capacity of horses and cattle? 



3. Name the various factors that influence the digestibility of feeding stuffs. 



4. How do (a) drying and (&) cooking affect the digestibility of protein? 



Give some examples. 



5. Give the influence of different nutrients on the digestibility of feeding 



stuffs. 



