FACTORS INFLUENCING THE WORK OF THE HORSE 289 



outgo was added that which passed thru the skin and vent as determined 

 by placing the animal in a Pettenkofer respiration apparatus. (72-4) 



450. Locomotion and carrying a load. Considerable energy is expended 

 by the horse in merely moving his body along a horizontal road, since he 

 must lift his body at each step and propel it forward. Yet in this work 

 of locomotion, no useful work is accomplished in the mechanical sense. 

 Zuntz found that when walking at a speed of 2.5 miles per hour, the 1,100 

 pound horse, carrying a 44-lb. harness, required 0.240 therm of net 

 energy in addition to the maintenance requirement when idle, for each 

 mile he traveled on a level road. When the horse carried a load of 220 Ibs. 

 on his back, the amount of net energy expended was increased 24 per ct. 

 above the amount required for the same distance and at the same speed 

 without a load. 



451. Work of draft, When the horse pulls a load and thus accomplishes 

 useful mechanical work, obviously he will expend more energy than when 

 merely moving his own body along a level road. Zuntz found that in 

 performing each 1,000 foot- tons of work of draft (which is about an 

 hour's work for a horse weighing 1,400 Ibs.) the horse expends 2.078 

 therms of net energy. 



452. Influence of speed on work. The horse is at his best for drawing 

 loads when moving at a rate of 2 to 2.5 miles per hour. If held to a 

 slower pace and especially if urged to move faster, his efficiency de- 

 creases, and he must expend more energy in doing a given amount of 

 work. Thus 26 per ct. more net energy was required in the trials of 

 Zuntz when a horse traveled a mile on a level road at a speed of 3.5 miles 

 per hour than when the same distance was covered at a speed of 2.5 miles 

 an hour. When his gait is increased to a trot, nearly twice as much 

 energy is required per mile of travel as at the slower walk. His efficiency 

 continues to become less as the speed increases, until when worked at a 

 speed of 11.25 miles an hour, he can accomplish less than one-tenth of the 

 amount of work he can perform at a moderate pace. 



Among the reasons why more energy is required to do a certain amount 

 of work at a fast pace are : (1) In trotting or galloping the rise and fall 

 of the body are much greater than in walking. Energy is wasted in these 

 movements, and hence a smaller amount is available for onward move- 

 ment. (2) At a rapid pace the work of the heart is increased, the 

 temperature rises, and much heat is lost thru the evaporation of water 

 from the skin and lungs in the effort to keep the body temperature 

 normal. The proportion of the food which produces heat is thus 

 increased, while less can be converted into work. 



Grandeau 12 states that a horse walking 12.5 miles per day was kept 

 in condition on a daily allowance of 19.4 Ibs. of hay, while a ration of 

 24 Ibs. was insufficient when the same distance was covered at a trot. 

 A horse hauling a load 12.5 miles daily at a walk was sufficiently 

 nourished by a ration of 24.6 Ibs. of hay, while one of 36.2 Ibs. all the 



u London Live Stock Journal. 1894, p. 49. 



