292 FEEDS AND FEEDING 



Most farm horses actually work but 1,000 hours a year, or less, the 

 average time worked per day being but 3 to 4 hours thruout the year. 

 However, during the rush seasons farm horses usually work long hours 

 and should then be classed as at hard work. (513) 



456. Severe work. The more severe the labor which the horse per- 

 forms, the larger must be the supply of net nutrients. Since the ration 

 must not have undue bulk, this necessitates a large proportion of concen- 

 trates, high in net energy content. On the other hand, the more severe 

 the labor, the smaller must be the allowance of roughage, for coarse feeds 

 are of low value for producing work, and when given in undue amount 

 hinder breathing, thru the distension of the digestive tract, thus placing 

 an increased burden on the already hard-worked animal. However, some 

 roughage must be supplied even during severe labor. (107) It must be 

 remembered that rich feed, carelessly administered, brings danger ; hence 

 especial care must be used in feeding the horse at severe work. 



457. Variations in body weight. During exercise and work a loss in 

 body weight occurs, due to the greater oxidation, or breaking down, of 

 the nutrients in the body and to the largely increased evaporation of water. 

 Grandeau and LeClerc 17 found that 2 horses lost on the average 2.3 Ibs. 

 each when walked for 148 minutes without drawing a load, while on haul- 

 ing a load at a trot for 79 minutes each lost 9.3 Ibs. A horse performing 

 a certain amount of work at a trot gave off 20.6 Ibs. of water vapor, nearly 

 twice as much as when doing the same amount of work at a walk, and over 

 3 times as much as when at rest. Such losses diminish the amount of 

 energy available for the production of work. 



When horses which have been idle for a period and consequently have 

 soft muscles are put at hard work, they will often lose 50 to 100 Ibs. in 

 weight, especially unless they are gradually accustomed to the work. Due 

 to the large capacity of their digestive tracts, the weights of horses or 

 cattle on consecutive days, taken at a uniform hour and under similar 

 conditions of feed and care, may vary 15 to 30 Ibs. or even more. This 

 shows the necessity of carrying on feeding experiments for considerable 

 periods of time and with several animals in order to escape, or rather 

 lessen, the errors which are introduced into the calculations thru ac- 

 cidental variations in the weights of the animals studied. 



458. Efficiency of the horse as a motor. Such a large part of the 

 mechanical power used on farms is furnished by horses that it is of 

 much interest to determine the efficiency with which they actually con- 

 vert into useful work the nutrients in the feed they consume. The 

 investigations of Zuntz show that the horse turns into useful work from 

 31 to 36 per ct. of the net energy he expends, in addition to that needed 

 to maintain his body when idle. This does not take into consideration 

 the energy of the food which is lost in the excreta, or in mastication, 

 digestion, and assimilation. (76-9) To gain a true idea of the efficiency 

 of the horse as a motor, we must compute his over-all efficiency, or the 



"Ann. Sci. Agron., 188, II, p. 276. 



