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 
How do steers and sheep differ in their ability to digest (a) coarse 
feeds; (b) concentrates? 
. What is the main difference in the digestive capacity of horses and cattle? 
. Name the various factors that influence the digestibility of feeding stuffs. 
. How do (a) drying and (b) cooking affect the digestibility of protein? 
Give some examples. 
. Give the influence of different nutrients on the digestibility of feeding 
stuffs. 
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