MAINTENANCE THE ENERGY REQUIREMENTS 297 



ternal work and regard the higher figures obtained in the winter 

 experiments as indicating a stimulation of the heat production 

 by the low temperature to which the animal was exposed ; i.e., 

 they consider that the experiments were made below the critical 

 temperature. The notably higher results obtained with lighter 

 rations they ascribe to a similar cause, viz., that the heat arising 

 from the work of digestion, together with that due to the neces- 

 sary internal work (fasting katabolism), was insufficient to 

 maintain the body temperature. 



It must be confessed that, in view of the more active, tem- 

 perament of the horse as compared with cattle this relatively 

 low figure for the fasting katabolism is rather surprising, and 

 the fact should not be overlooked that it is derived from short 

 periods in which it is probable that the animal was unusually 

 quiet. It perhaps represents more nearly the physiological 

 than the economic minimum of net energy required for main- 

 tenance, and it would be of much interest to compare it with 

 the results of 24-hour experiments. 



386. Metabolizable energy in maintenance rations. A 

 considerable number of experiments are on record in which 

 the amount of total digestible matter required for the main- 

 tenance of the horse has been determined. 



The maintenance rations of cattle and sheep may be deter- 

 mined with a good degree of accuracy by varying the quantity 

 of feed given until equality between income and outgo or con- 

 stancy of live weight is attained, but this method is not fully 

 applicable to the horse. Owing to his more active tempera- 

 ment, feed seems to exert a greater stimulus upon his muscular 

 activity than is the case with the more phlegmatic ruminants, 

 so that a considerable excess over an actual maintenance 

 ration may be consumed by a horse and expended in the 

 various minor activities noted in Chapter VII (348), while 

 the balance of income and outgo may show neither gain 

 nor loss, i.e., may appear to show that the ration is a main- 

 tenance ration. 



a. Wolff's determinations. One method of avoiding this 

 difficulty and determining the true maintenance ration is that 

 employed by Wolff in his extensive investigations 1 upon work 

 production by the horse (670, 779). In these experiments the 



1 Compare the writer's Principles of Animal Nutrition, pp. 531-535- 



