56 



Experiment Station Bulletin 345 



Studies on Energy Expended by a Horse at Work 



These studies have been continued during the year by measuring the 

 effect of speed on the energy expended by the horse. A long series of 

 experiments was carried out with a Morgan mare to determine the com- 

 parative amount of energy expended when standing quietly, walking, ana 

 trotting at different speeds with and without carrying a rider. 



The results showed that quietly standing required 9 calories per min- 

 ute; walking at a moderate speed increased it to 26 calories; at a slow 

 trot (1 mile in 8 minutes) raised it to about 50 calories, and increasing the 

 speed still further (1 mile in 4 minutes) brought it up to 75 calories, or 

 over eight times the standing value. The energy cost of carrying a rider 

 (weighing with saddle, etc., 175 pounds) at a walk increased 30 per cent, 

 but at a trotting speed of 5.4 minutes per mile the cost of carrying this 

 weight increased it 75 to 80 per cent over trotting without load. 



Likewise, in the case of larger draft horses pulling loads, the energy 

 cost increased per pound pull from 14.5 calories at 160 pounds resistance 

 to 25.0 calories at 250 pounds resistance, the speed of walk being the same. 

 Based on a continuous effort of one hour, the energy expended to pull at 

 160 pounds resistance was 2,300 calories, but at 250 pounds resistance it 

 was 6,260 calories, or nearly trebled. 



The result of primary interest in the comparative amount of energy 

 spent at different degrees of exertion is observed in the tremendous in- 

 crease in the energy cost of work when the rate or speed at which the 

 work done is increased. 



Physical effort is expensive in energy cost, and any economies that 

 may be necessary must be obtained by management, the prevention of 

 waste by unnecessary effort, and possibly by some substitutions in the 

 character of the feed rather than in the amount. 



Fig. 5. Peacetime Study of Energy Expended by Horse at Work 



