200 UTILISATION OF FOOD BY THE ANIMAL [chap. 



of hay would keep it in condition ; if it drew a load that 

 added 1943 foot-tons to its work, 26-4 lb. of hay were 

 needed ; while 24 lb. were insufficient if the horse trotted 

 without a load. The load meant 6-4 lb. extra of hay, 

 and according to our table a better effect would have 

 been produced by substituting 2 lb. of maize. 



It is difficult as yet to apply these kind of calcu- 

 lations to practice because of the impossibility of 

 estimating with exactitude the amount of work 

 performed by a horse in any operation, but we may 

 assume that at ordinary heavy work like ploughing, a 

 horse will be doing about 1000 to iioo foot-tons of work 

 per hour. To do this work, 2 lb. of maize, 2\ lb. of 

 beans, or nearly 3 lb. of oats will be required ; or for an 

 eight-hour day's work, about 20 lb. of mixed corn. To 

 this must be added, not the whole maintenance require- 

 ment of the horse, because his heat requirements will be 

 satisfied by the development of heat from the muscular 

 work spent in the body and in digestion, but instead 

 about a third of the whole amount in order to do the 

 work of respiration and circulation, i.e. about 3 lb. more 

 of corn. If some of this corn is replaced by its 

 equivalent in hay we get a fair approximation to the 

 ordinary working rations of a farm horse, and these can 

 be adjusted on the principle that every hour's work is 

 equivalent to between 2 lb. and 3 lb. of corn. These 

 figures are contained more exactly in the following table, 

 derived from Kellner, where the horse is made to work 

 under experimental conditions, walking at the rate of 

 about 2\ miles per hour, against the draught indicated, 

 for eight hours a day. 



The concentrated foods like oats, beans, or maize yield 

 very nearly their full value in starch equivalents for all 

 the digestible constituents of the food, i.e. nearly all the 

 digestible constituents are available for work. But, as 



