Principles of Feeding 55 
of the surrounding atmosphere, and its maintenance requires 
much heat, as the body is continually giving off heat. The body 
tissues become worn out and must be constantly renewed by the 
matter and energy from the food. In the case of young animals, 
there is a constant formation of new tissue. This requires more 
matter than energy. Again, the muscular function of vital pro- 
cesses requires much energy, which must be supplied by the food. 
Of the total amount of food that an 
animal will ordinarily consume, a 
very large proportion goes to sup- 
port life and a small amount to 
production. 
103. Composition of food.— The 
value of a food depends, among 
other things, on its composition. 
There is a tendency to ignore the 
fact that a food should be con- 
sidered with reference to its compo- 
sition. It is assumed that a pound 
of timothy hay, for example, is equivalent to a pound of clover hay, 
when as a matter of fact their composition is such as to make them 
widely different, so that one will not take the place of the other. 
The number of compounds found in the food is very large, and 
many of them are very complex in their nature. For convenience 
in comparing foods, these compounds are grouped into classes. 
These classes are few in number, easy to comprehend, and serve 
the purpose well from a practical point of view. We recognize 
five distinct groups, one of which is divided into two sub-groups. 
They are as follows : — 
Fic. 31.— Percheron stallion. 
1. Water 
2. Ash (mineral compounds) ] 
3. Protein (nitrogenous compounds) | | Dae 
Carbohydrates ied ! Nutrients | matter 
4. Carbohydrates | Nitrogen-free extract | 
5. J A 
Fats 
