390 THE FEEDING OF ANIMALS 



applicable to horses under all conditions of labor. More- 

 over, it is clearly demonstrated by two investigators 

 that the food energy required for a unit of work increases 

 with the speed. In other words, a horse that trots 20 

 miles a day must have more food than when he walks the 

 20 miles. In the same way draft animals require food 

 somewhat in proportion to the pace with which they 

 travel over a given distance. Grandeau has shown that a 

 horse was kept in condition with 19.4 pounds of hay when 

 he walked 12J^ miles, but 24 pounds was insufficient 

 when he trotted the same distance. Zuntz measured the 

 oxygen used for each kilogram meter when a loaded horse 

 traveled at different velocities. When the pace was 3 

 miles an hour, with a load of 275 poimds, the energy 

 required was equal to 4,600 calories for each kilogram 

 meter of horse, which increased to 7,753 calories when the 

 speed reached 6J^ to 73^ miles an hour. The food needed 

 for a unit of work increased nearly 70 per cent in increas- 

 ing the speed from 3 to 7 miles. Zuntz shows that if 

 a horse exerts himself to the utmost the use of oxygen 

 rises at a rapid rate, and that the food consumed for a imit 

 of work is nearly one-half more than with ordinary draft. 

 It appears to be a rule that as the intensity of exertion 

 of thfe horse increases the food cost of a given amount 

 of labor performed increases. Men of experience recog- 

 nize this fact in a general way when they insist on favor- 

 ing their animals to the slowest pace that is consistent 

 with the conditions involved. 



484. The food requirements of a worMng horse. — 

 There are two general ways of ascertaining the food needs 

 of a working horse: by practical experiments in which the 

 rations are varied until a conclusion is reached as to what 

 will support an animal under given conditions, and by 



