278 PRODUCTIVE FEEDING OF FARM ANIMALS 
in the muscles goes on faster than the repair of muscles from the 
feed supplied, the horse will lose weight. This frequently happens 
when a horse is working hard for a considerable period of time and 
does not receive a sufficient quantity of easily digestible feed (con- 
centrates). 
Character of Feed Required.—As the muscles are largely com- 
posed of proteins, it might be supposed that the decomposition of 
protein in the body would increase with the amount of labor per- 
formed; such is not the case, however. The oxidation of non- 
nitrogenous materials in the body, on the other hand, increases 
rapidly when hard work is done. .A part of the energy thus set 
free appears as heat, and another part as mechanical work. The 
oxygen required for the oxidation processes going on in the body is 
Fig. 68.—Draft horses that give a good account of themselves in the show ring, as breeding 
animals and for doing heavy work. (Pacific Rural Press.) 
supplied by the blood, and the oxidation products formed, carbon- 
dioxide and water, are exhaled through the lungs and in the per- 
spiration. The result of heavy work is, therefore, seen in an in- 
creased consumption of oxygen and an increasing excretion of 
carbon-dioxide and water. This is also what takes place when 
mature fattening animals are gaining weight. The carbohydrates 
or fat, or both, are the main sources of energy supply both in the 
production of body fat and muscular energy, and it is not neces- 
sary to furnish more protein to working animals than in the case 
of fattening animals, viz., sufficient to insure a complete digestion 
of the feed. For this purpose a nutritive ratio of 1:8 or 1:10 
will suffice. 
A growing animal that is performing work requires a special 
supply of protein, and the same appears to be the case with race 
horses or driving horses which perform heavy work within a short 
