65 



same, and found that it varied from 6.4 pounds with a horse at restto" 

 20. 6^ pounds with a horse trotting and drawing a load. (See also p. 38.) 

 The heat required for the evaporation of this amount of water is 

 quite large and necessitates the combustion of a considerable amount 

 of nutritive material in the body, thus diminishing the quantity of 

 material available for the production of work. 



EFFECT OF MUSCULAR WORK ON DIGESTIBILITY. 



Grandeau's and Leclerc's experiments also indicate that the kind of 

 work performed has some effect on digestibility. If the total amount, 

 of organic matter digested while at rest be represented by the number 

 1,000, the proportion digested during different kinds of work is showny 

 they consider, by the following table: 



Relative proportion of total organic matter digested by horses at different conditions of rest 



a)id irork. 



At rest 1,000 



Walking 1 , 032 



At work walking 1 . 007 



Trotting 976 



At work trotting 973 



Drawing a cab 959 



"We see here that the moderate exercise is accompanied by a small but distinct 

 improvement in the digestive functions, but that as soon as trotting commences 

 digestion becomes less efficient than when at rest, while hard work while trotting 

 still further diminishes the proportion of food digested. When we look into the 

 details we find that the starch and sugar in the food are perfectly digested under all 

 conditions of labor. The digestibility of the fat increases with exercise and does not 

 diminish by labor below the point reached in repose. The digestibility of the 

 albuminoids increases rather considerably with exercise and diminishes sharply 

 when trotting commences. The principal matters usually grouped as soluble car- 

 bohydrates, but which in this case are merely the more digestible constituents of 

 the fiber, undergo the greatest amount of variation, their digestibility rising consid- 

 erably with exercise and falling still more considerably with hard labor. In the 

 case of the more soluble portion of the fiber there is no rise in digestibility by exer- 

 cise; the maximum rate of digestion is here obtained in repose, and diminishes con^ 

 siderably with increased bodily exertion. On the whole it appears that the constitur 

 ents of the food which are most affected by rapid exertion are those whoi-e digestion 

 takes place to a large extent in the lower part of the intestines; the motion of the 

 horse probably determines their more rapid progress through the system. 



From the results of earlier experiments with German farm horses, 

 Wolff, Kellner, and associates'^* concluded that nuiscular work dimin- 

 ished digestibility little, if at all. The coefficients of digestibility of 

 the ration when work was performed were slightly lower, y)ut the dif- 

 ferences were so small that they are regarded as of no importance. 

 Grandeau's and Leclerc's values are within 3 per cent of those found 

 by Wolff, and it seems fair to say that from a practical standpoint the 

 diminished digestibility due to muscular work is not very important. 



«Landw. Jahrb., 8 (1879), sup. I., p. 73. 

 17399— No. 125—03 5 



