104 FEEDS AND FEEDING 



for work animals is for a sufficient supply of feeds rich in easily di- 

 gested carbohydrates, and which consequently yield a large amount of net 

 energy. Hence the most common rations for horses at hard work are 

 made up of only a moderate amount of hay or other roughage, with a 

 liberal supply of farm grains, such as oats, corn, or barley, which are 

 rich in net energy. If the rest of the ration is very low in protein, a 

 small amount of protein-rich feeds should be added to balance the ration 

 according to the recommendations of the feeding standards. The harder 

 the labor performed, the larger should be the proportion of grain to 

 roughage in the ration. Detailed discussions of the feed requirements of 

 horses for various classes of work are given in Chapters XVI 1 1 and XX. 

 (454-6, 530, 536-8) 



142. Factors influencing energy required for work. The amount of en- 

 ergy required to produce a given amount of useful work depends upon 

 many factors. Practice in doing a certain kind of work lessens the 

 amount of energy expended. For instance, in experiments upon him- 

 self Gruber 5 found that after training for 2 weeks the energy he used 

 in climbing a certain tower was decreased by over 20 per ct. On the 

 other hand, experiments by Lowy 6 and by Zuntz 7 show that fatigue 

 causes a considerable increase, ranging from 14 to 41 per ct., in the 

 amount of energy expended in performing a given amount of work. 

 This is largely due to the fact that with increasing fatigue the muscles 

 normally used, and which are thus most efficient in performing the given 

 work, are put out of use. Then other less used muscles are called upon 

 to a constantly increasing degree, and these cannot perform the work 

 so economically. 



The part of the expended energy appearing in useful work also varies 

 with the build of the animal, the development of its muscles, and the 

 structure of its limbs. For example, Zuntz found that a lame horse 

 expended 99 per ct. more energy in traveling a given distance than a 

 sound one. In the work of climbing a grade he found a variation with 

 different horses of as much as 52 per ct. in the proportion of the total 

 energy expended which appeared as useful work. An animal which is 

 able to accomplish one form of work most economically may have to 

 expend an unusual amount of energy on other kinds of work. For 

 example, horses bred for generations to the saddle can carry the rider 

 with a smaller expenditure of energy than those whose breeding, form, 

 and qualities specially fit them for draft purposes. 



Certain forms of labor are performed with greater economy of energy 

 than others. Katzenstein 8 found in experiments with men that about 

 65 per ct. more energy was used in turning a wheel with the arm than 

 was required when the same work was done with the leg. 



The experiments by Zuntz show that increasing the speed at which 

 work is done also lessens the efficiency with which it is performed. This 



6 Ztschr. Biol., 38, 1891, p. 466. T Landw. Jahrb., 27, 1898, Sup. III. 



'Arch. Physiol., 49, 1891, p. 413. 8 Wolff, Farm Foods, p. 84. 



