IX.] DIGESTIBILITY 177 



how much more capable are sheep and cattle, with their 

 complex stomachs, ruminating habits, and lengthy 

 intestines, to deal with fibrous foods than are horses or 

 even pigs, in the intestine of which animals the food 

 remains for a much shorter period. Hence the digesti- 

 bility of many foods depends upon the animal to which 

 it has been fed, but these variations occur much more in 

 dealing with such bulky foods as hay or straw than 

 with the concentrated feeding stuffs. Of course, varia- 

 tions occur in the food itself; for example, hay cut before 

 it is dead ripe is the most digestible, and the nitrogenous 

 matter of hay is better digested when the food is 

 rich in this constituent. In fact, we may say 

 generally that rich foods are better utilised than poor 

 ones, without regard to the fact that they contain initially 

 a higher proportion of valuable constituents. Only when 

 an excess of food is given does its digestibility decrease, 

 a starving animal cannot get more than the normal 

 amount of nutriment out of a given food. Again, the 

 work that the animal is doing has little or no effect 

 upon the digestibility of the food given to it. Cooking 

 does not appear to increase the digestibility of any of 

 the usual cattle foods ; in fact, the digestibility of the 

 proteins is reduced. Drying the food, as in making hay 

 from grass or in curing maize forage, does not diminish 

 the digestibility if the process is properly carried out. 

 Making the grass into silage, so far from incre£ising, 

 actually reduces the digestibility of such proteins as 

 escape reduction to a-proteins by the process ; it is a 

 mistake to suppose that silage-making will convert 

 worthless grass and similar waste products into valuable 

 food. It has also been shown that while the addition 

 of fats or proteins to a comparatively poor diet of 

 hay and straw and roots causes no reduction in the 

 digestibility of either the original diet or the additions, 



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