WORK PRODUCTION 565 



of 100 pounds, 15 miles per day, including 5 miles up a i per 

 cent grade, at a speed of 3! miles per hour. The mechanical 

 work performed consists of lifting the weight of the animal plus 

 the load 264 feet and in overcoming a draft resistance of 100 

 pounds through 79,200 feet. The total mechanical work, there- 

 fore is as follows : 



TABLE 158. EXAMPLE OF COMPUTATION OF WORK DONE 



Draft 100 X 5280 X 15 = 7,920,000 foot pounds = 2.565 Therms 



Ascent 3100 X 264 = 818,400 foot pounds = 0.265 Therms 



Total 8,738,400 foot pounds = 2.830 Therms 



The amount of body energy which the horse must metabolize 

 in the performance of this daily task will be that corresponding 

 to the mechanical work of draft and of ascent, computed from 

 the percentages in Table 155, together with the energy ex- 

 pended in locomotion according to the same table and the energy 

 requirement for maintenance. The total requirement of net en- 

 ergy per day, therefore, will be as follows : l 



TABLE 159. EXAMPLE OF COMPUTATION OF NET ENERGY REQUIREMENT 



For draft 2.565 -f- 0.313 = 8.195 Therms 



For ascent 0.265 -*- 0.343 = 0.773 Therms 



For locomotion 0.262X15 = 3.930 Therms 



For maintenance (385) 4-356 Therms 



Total 1 7. 254 Therms 



673. Calculation of rations. Having in some such way as 

 that just illustrated determined the net energy requirement of 

 the work horse it is evident that the corresponding ration may 

 be computed if the net energy values of the feeding stuffs to be 

 used are known. Unfortunately, in the case of the horse, the 

 principal work animal of the United States, such net energy values 

 of feed stuffs as we now possess have not been directly deter- 

 mined but are the results of somewhat complicated calcu- 

 lations (775-778) . For the ox, on the contrary, fairly satisfactory 

 data regarding the net energy values of feed stuffs are available 

 (760, 773, 774), but in this case very few determinations of the 

 efficiency of the animal's body in work production have yet been 



1 The computation could be somewhat simplified by assuming a uniform net 

 efficiency of 5 for all forms of work. 



