148 THE CHEMISTRY OF CATTLE FEEDING 



of horses. It will presently be shown that this is a very 

 variable quantity ; but assuming that an animal did work at 

 that rate, the amount of food required to provide the energy 

 can be calculated from the data given, i.e. by the formula. 



The normal day's work for a horse is 8 hours = 28,800 

 seconds; and at 550 foot-pounds in each second, the total 

 amount of work done would be 15*84 million foot-pounds. 

 Applying the formula D = 2'i6W, we have [15-84 X 2-16 =] 

 34*21 kt. as the amount of dynamic energy to be supplied in 

 the food. If the animal does not consume enough food to 

 supply that amount of energy in addition to a sufficient main- 

 tenance ration, it cannot work for eight hours at the rate 

 assumed without loss of weight. 



Of course it is not usually possible to apply the formula to 

 animal work in this simple manner, because in ordinary prac- 

 tice it is extremely difficult to estimate, with any degree of 

 accuracy, the amount of work done. We are, therefore, com- 

 pelled to revert to such vague, empirical standards as light, 

 medium, and heavy work. 



The total amount of work done in any case is expressed 

 by the formula 



W = PX VX T 



where W is the work (in foot-pounds), P the effort (in pounds), 

 V the velocity (in feet per second), and T the time (in seconds) 

 occupied; PV is, of course, the rate (in foot-pounds per 

 second) at which the work is done, i.e. the total work done in 

 i second. The following examples will make this plain : 



When the work is done wholly against gravity, the effort, 

 P, is represented simply by the weight (in pounds) of the sub- 

 stance raised. In many parts of Canada and elsewhere the 



