2 go NUTRITION OF FARM ANIMALS 



The fasting katabolism of such an animal may, however, 

 be computed in the manner already described (374) from a 

 comparison of two periods on different amounts of the same 

 feed, or ration, both being less than that necessary for main- 

 tenance. Twenty-three experiments of this sort, on nine 

 different steers, only one of which was fat, in which the rela- 

 tive metabolism of the animals when standing and when lying 

 was determined, have been made by Armsby and Fries. 1 Com- 

 puted per 1000 lb., in proportion to the two-thirds power of 

 the live weight (347) and corrected 2 to a uniform period of 1 2 

 hours standing out of the 24, the net energy requirements were 

 as shown in Table 47. No other experiments on precisely this 

 plan have yet been reported. 



Even if a few seemingly extreme results, like those of 1902 

 and 1912 be excluded, the figures show a wide range. The 

 trials with mixed rations of roughage and concentrates show 

 on the whole somewhat higher results than those with rough- 

 age only, but the experiments are hardly numerous enough to 

 show whether this difference is significant. 



381. Net energy in maintenance rations. A considerable 

 number of earlier experiments are also on record in which the 

 amounts of net energy contained in actual maintenance rations 

 of cattle may be computed with more or less accuracy. 



The early experiments of Henneberg and Stohmann, on which 

 was based Wolff's feeding standard for maintenance long cur- 

 rent, as well as a considerable number of subsequent ones, 3 

 have now chiefly an historic interest. Of the later investiga- 

 tions, by far the most important are those by G. Kiihn and by 

 Kellner 4 in which approximate maintenance rations were fed. 

 The small gains or losses of protein and fat by the animals were 

 determined by means of a Pettenkofer respiration apparatus 

 and corrected for upon the basis of results obtained in other 

 respiration experiments on productive rations, and in this way 

 the metabolizable energy required for maintenance was com- 

 puted. 



1 Eight of them have been reported. U. S. Dept. Agr., Bur. Anira. Indus., 

 Buls. 74, 101, and 128. 



2 In the manner described in Jour. Agr. Research, 3 (1915), 454. 



3 Compare Penna. Expt. Sta., Bui. 42 (1898)', pp. 8-21. 



4 Reported by Kellner : Landw. Vers. Sta., 53 (1900), pp. 6-16. 



