40 



In addition to other matters, this same investigator noted that the 

 body conformation had a marked effect on the economical production 

 of work. He found that defects in external conformation and move- 

 ments necessitate an increased amount of muscular exertion. This 

 has an important bearing upon the market value of the horses. Too 

 low a stall temperature also increases the amount of material required 

 for maintenance. In many cases observed this increase was hardly 

 covered by 2 pounds of oats daily. 



PROPORTION OF ENERGY OF FOOD EXPENDED FOR INTERNAL 

 AND EXTERNAL. MUSCULAR WORK. 



A horse converts 38.3 percent of the energy of food into mechanical 

 work. On account of the energy required for respiration, the beating 

 of the heart, etc., only about 34 per cent of the energy of the food is 

 actually available for external muscular work. The best, record for a 

 steam engine is said to be an efficiency per indicated horsepower of 

 22.7 per cent on the basis of total heat supply. Per delivered horse- 

 power the amount is probabl}^ 10 per cent less. The animal is, there- 

 fore, seen to be a much more efficient machine than the engine. 



ENERGY REQUIRED TO CHEW AND DIGEST FOOD. 



One of the most interesting of the lines of investigation followed in 

 an extended series of experiments, carried on under the direction of 

 Professor Zuntz at the Agricultural High School in Berlin, was the 

 determination of the energy required to chew and digest different 

 foods. The experiments were complicated and too extended to describe 

 here except in very general terms. They showed that the respiratory 

 quotient, i. e. , the ratio of the carbon dioxid excreted in the breath to 

 the oxygen consumed from the air is a very delicate index of the 

 changes which take place in the body. It was found that the internal 

 muscular work expended in chewing, swallowing, and digesting food 

 could be determined by the variations in the respiratory quotient and 

 in the amount of carbon dioxid excreted when this kind of work was 

 performed, as compared with the amount when the animal rested. 

 Different feeding stuffs modified the respiratory quotient in different 

 ways, and it was evident that some required more labor for diges- 

 tion and assimilation than others. This is a matter of considerable 

 importance, for it is evident that if two feeding stuffs of practically 

 the same composition are digested with equal thoroughness but one 

 requires for digestion and assimilation the expenditure of more 

 internal muscular work than the other, it is really less valuable; in 

 other words, the two may contain the same amount of digestible 

 nutrients, l)ut one causes the body more labor to assimilate than 

 the other. On the basis of Zuntz's average figures of composition and 

 digestibility, 1 pound of hay furnishes 0.391 pound of total nutri- 



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