56 



MAINTENANCE RATIONS OF FARM ANIMALS. 



single summer period it reaches the minimum of 3.970 therms. Zuntz 

 and Hagemann consider that the latter represents approximately 

 the minimum requirement for internal work and regard the higher 

 figures obtained in the winter experiments as indicating a stimula- 

 tion of the heat production by the low temperature to which the 

 animal was exposed. The notably higher results obtained with the 

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

 arising from the work of digestion and from the necessary internal 

 work (fasting katabolism) was insufficient to maintain the body 

 temperature. Accordingly, they regard the differences shown in col- 

 umn 8 of the foregoing table as including in these cases not only the 

 minimum necessary for internal work but also an expenditure for 

 heat production. In other words, they consider that the critical tem- 

 perature ( compare p. 71 ) for the horse is high as compared with that 

 for cattle, and the critical amount of food small (compare p. 73). 

 Earlier experiments 1 upon another horse in which lighter rations 

 were fed confirmed this conclusion. 



On the average of the 8 most satisfactory experiments out of 12, the esti- 

 mated total katabolism per day and head was 11.027 therms upon a ration 

 consisting of 3.5 kilograms of oats, 0.5 of straw, and 2.5 of hay. Computed in 

 the same manner as in the foregoing examples, the expenditure of energy in 

 the digestion of this ration is equal to 3.782 therms, which leaves a remainder 

 of 7.244 therms, equivalent to 140.3 gram-calories per square centimeter of sur- 

 face. This is a higher figure than any of those contained in the foregoing table, 

 although the total katabolism was not notably different. The authors conclude, 

 therefore, that the small amount of heat liberated by the digestive work was 

 compensated for by an increased katabolism of body tissue. 



From a balance experiment on the same animal in the respiration apparatus 

 cf the Gottingen Experiment Station they also compute 2 the metabolizable 

 energy required for maintenance by subtracting from the total nutrients di- 

 gested the fat equivalent of the protein and fat gained by the animal. They 

 thus reach a maintenance ration per 500 kilograms, live weight, of 3.265 

 grams digestible nutrients, equivalent to 12.93 therms. Their final conclusion 

 (loc. cit, p. 420) is that their animal required per head at least 11 therms, or per 

 500 kilograms live weight 12.10 therms, of heat to maintain his body tempera- 

 ture. In other words, this is the minimum of metabolizable energy which must 

 be supplied in a maintenance ration, since if less be present, even although the 

 ration supplies the requisite amount of available energy, body tissue will still 

 be katabolized for the production of the heat necessary to maintain the body 

 temperature. 



Computed to 1,000 pounds live weight in proportion to the two- 

 thirds power of the latter, Zuntz and Hagemann's maintenance 

 ration is : 



1 Landvvirtschaftliche Jahrbiicher, vol. 18, p. 1 ; vol. 27, Erganzungs Band III, pp. 

 356-257. 



2 Ibid., p. 423-424. 



Available energy for internal work 



Additional required for heat production 



Therms. 

 _ 4.08 

 _ 7. 80 



Total metabolizable energy required. 



11. 88 



