258 Feeds and Feeding. 



396. The work of the horse. That work which the horse per- 

 forms may be resolved into: 



(1) Locomotion, or advancing the body along a level course. 



(2) Lifting the body, with or without a load, against the force 

 of gravity in ascending a grade. 



(3) Carrying a load. 



(4) Draft, or hauling a load. 



Zuntz 1 determined the amount of energy expended in these vari- 

 ous forms of work at different speeds and under varying conditions. 

 His more important findings are presented in articles which follow. 



397. Locomotion. The horse weighing 1100 Ibs. including har- 

 ness expends the following amounts of energy in moving his body 

 1 mile along a level road at various speeds: 



Walking" at a speed of 2. 9 miles per hour 0. 26 therm 



Walking at a speed of 3. 4 miles per hour 0. 29 therm 



Walking at a speed of 3. 7 miles per hour 0. 32 therm 



Trotting at a speed of 7. 3 miles per hour 0. 44 therm 



It is shown that increasing the walking speed causes a consider- 

 able increase in the amount of energy expended in moving a mile. 

 Trotting at a speed of 7.3 miles per hour causes the expenditure of 

 69 per ct. more energy than walking at a speed of 2.9 miles per hour. 



Since in locomotion the body of the horse is alternately raised and 

 lowered, it is difficult to measure the actual amount of mechanical 

 work performed in order to compare it with the energy expended. 

 Computations by Zuntz indicate that about 35 per ct. of the total 

 energy expended by the horse moving on the level is actually trans- 

 formed into the external work of advancing his body, the remainder 

 of the energy producing no external work, but taking the form of 

 heat. (112) 



398. Influence of grade. When the tread power was set so that 

 the walking horse ascended a grade of 10.7 ft. in 100 at a speed of 

 3.1 miles per hour, Zuntz found that more than 3 times as much en- 

 ergy was expended as when walking the same distance on the level 

 at a slightly faster pace. When the still steeper grade of 18.1 ft. in 

 100 was ascended on the tread power at a speed of only 2.8 miles 

 per hour, nearly 5 times as much energy was expended as when mov- 

 ing on a level course. 



In going down a gentle incline, owing to the pull of gravity, less 

 energy was expended than in moving: on a level road, resulting in a 



1 Landw. Jahrb., 27, Sup. Ill ; Kellner, Ernahr. landw. Nutztiere. 



