382 FEEDS AND FEEDING 



free extract because it contains no nitrogen. The 

 carbohydrates are all formed from CO 2 in the air with 

 varying proportions of H 2 O. (See page 34.) 



Fat or Ether Extract. - - The fats have the same 

 functions as the carbohydrates furnishing to ani- 

 mals in a condensed form energy and fat. It is 

 because of the fact that fats are two and one fourth 

 times as strong, pound for pound, in producing heat 

 as other carbohydrates, that they are considered sepa- 

 rately in feeding. In the carbohydrates the carbon 

 is combined with hydrogen and oxygen in proportion 

 to form water, whereas the carbon in fats is not so 

 combined. 



The term ether extract is a little more accurate than 

 fats. In the tables compiled the fats not only include 

 what are known as fats, but all the dry matter that can 

 be dissolved out by ether. (See page 34.) Besides fat 

 they include wax and chlorophyll. 



Digestibility. Not all the food elements in a food 

 stuff are available for the use of the animal. Much 

 depends upon the digestibility of the food. The di- 

 gestibility of the food itself varies according to the 

 time it is harvested ; hay, for instance, should be cut 

 and cured just before its seeds have ripened, while grain 

 should be harvested when it is ripe. 



Digestibility varies with different classes of animals. 

 Cattle and sheep will digest a larger percentage of rough- 

 age than horses or pigs. It varies slightly also with 

 different animals of the same class, depending on the 

 age and on the individual peculiarities. Some animals 

 are easy keepers, because they digest and assimilate a 

 relatively larger proportion of the food that they eat 

 than others. 



