24 



MAINTENANCE RATIONS OF FARM ANIMALS. 



As was to have been expected, the work of mastication proves to be much 

 greater in the case of hay than in that of grain. Maize gave a remarkably low 

 result, while the lowest was obtained with green fodder. Even when the results 

 on the latter are computed per kilogram of dry matter, they are still about 40 

 per cent lower than those on hay. A few experiments on old horses with defec- 

 tive teeth gave somewhat higher results for the mixture of oats and cut straw. 



While pointing out that, as the above results show, other factors than the 

 amount of crude fiber influence the work of mastication, they nevertheless 

 believe that a sufficiently close approximation for practical purposes may be 

 reached by computing the work of mastication upon the amount of crude fiber 

 present, which gives an average of 0.565 calorie per gram, and using this factor 

 to compute the work of mastication of the average ration. Adding this factor 

 to the 2.086 calories computed for the work of digestion of one gram of fiber 

 gives a total of 2.65 calories per gram of total crude fiber as representing the 

 work of mastication together with the extra expenditure of energy in digestion. 



In brief, then, Zuntz and Hagemann compute the available energy, 

 or maintenance value, of a feeding stuff for the horse as follows: 

 First, the metabolizable energy is computed at the rate of 3.96 calo- 

 ries per gram of total digestible matter, including the digestible crude 

 fiber and the digestible fat multiplied by 2.4. Second, from the 

 metabolizable energy thus computed there is subtracted 9 per cent 

 for the work of digestion and in addition 2.65 calories for each gram 

 of total crude fiber present. 



The method of computation may be conveniently illustrated from 

 the data given by Langworthy 1 for timothy hay. Zuntz and Hage- 

 mann 's factors, recalculated per pound for convenience, become, for 

 metabolizable energy, 1.796 therms ; for crude fiber, 1.202 therms. On 

 this basis the calculation of the available energy of the hay would be 

 as follows: 



COMPUTATION OF AVAILABLE ENERGY. 



Available energy in 100 pounds of timothy hay. 



Digestible nutrients : 



Protein 



Crude fiber 



Nitrogen-free extract 

 Fat (1.18X2.4) 



Pounds. 



1. 25 

 12. 39 

 21. 29 



2. 83 



Total crude fiber. 



37. 72 

 29. 00 



Therms. 



Metabolizable energy (1.796 therms X 37.72) 



Work of digestion : 



9 per cent of metabolizable (67.75 therms X 0.09) 

 Additional for crude (1.202 therms X 29) 



67. 75 



/ 



Therms. 

 _ 6.10 



_ 34.86 



Total 



40. 96 



Available energy (maintenance value) 



26. 79 



1 U. S. Department of Agriculture, Office of Experiment Stations, Bulletin 125, p. 14. 



