68 



MAINTENANCE RATIONS OF FARM ANIMALS. 



enough, this animal showed the lowest maintenance ration of the 

 three fattened animals and, moreover, one which is distinctly less 

 per unit of computed surface than in the unf attened state, viz : 



Uufattened 14. 72 therms metabolizable energy per 1,000 pounds live weight. 



Fattened 13. 86 therms metabolizable energy per 1,000 pounds live weight. 



No other respiration experiments upon the relative maintenance 

 requirements of fattened and unf attened animals are on record. 

 Evvard's live-weight results, however, as given in the table on page 

 47, appear to confirm Kellner's conclusion that the relative mainte- 

 nance ration of fattened animals is greater than that of the same 

 animals unfattened. 



One obvious reason why the maintenance requirement should be 

 greater in the former case is the presumably greater muscular effort 

 expended in standing, due to the greater weight to be supported. 

 Zuntz and Hagemann in experiments upon the horse carrying weight 

 on its back found that this increase was proportional to the amount of 

 weight added. The increase indicated by Kellner's averages, how- 

 ever, is greater than would be computed on this assumption, and the 

 same is true of Evvard's fat animals, the difference becoming greater 

 as the animals become fatter. 



AGE. 



The energy requirement of a young animal is naturally smaller per 

 head than that of an older animal on account of the difference in 

 size. Whether there is any difference in the relative requirements — 

 that is, in the requirement computed to uniform weight or surface — 

 is not altogether clear, few specific results on farm animals being on 

 record. Evvard's results on yearlings, page 46, are somewhat higher 

 than most of the results which have been obtained with mature 

 cattle, although, of course, these figures do not refer to the same 

 individuals at different ages. Armsby and Fries, 1 in a series of respi- 

 ration calorimeter experiments upon the same two animals in three 

 successive years, observed a progressive decrease in the maintenance 

 requirement of yearlings, 2-year-olds, and 3-year-olds when corrected 

 to a uniform number of hours standing and computed to equal ex- 

 ternal surface (that is, in proportion to the two-thirds power of the 

 weight ) . 



Somewhat extensive data are on record regarding the metabolism 

 of man at different ages. A summary and discussion of these by 

 Tigerstedt 2 seem to show clearly that, leaving out of account infants 

 and very aged persons, the metabolism per unit of surface diminishes 

 from youth to maturity. In view of the slow development of man, 

 these results are comparable to such as might be obtained during the 

 first 6 to 12 months of the life of ordinary domestic animals and for 



1 Bureau of Animal Industry, Bulletin 128, p. 55. 



2 Nagel's Handbuch der Physiologie des Menschen, I, 469. 



