8 



MAINTENANCE RATIONS OF FARM ANIMALS. 



it appears desirable to practice it the observation of the skilled 

 stockman, especially if supplemented by occasional weighings, will 

 usually suffice to determine whether or not the end is being attained. 

 Nevertheless, the subject has significance for practice as well as for 

 science. A very considerable fraction of the feed actually con- 

 sumed by farm animals — on the average probably fully one-half — 

 is applied simply to maintenance. But if half of the farmer's feed 

 bill is expended for maintenance, it is clearly important for him to 

 know something of the laws of maintenance — how its requirements 

 vary as between different animals, how they are affected by the con- 

 ditions under which animals are kept, how different feeding stuffs 

 compare in value, etc. — as well as to understand the principles gov- 

 erning the production of meat, milk, or work from the other half of 

 his feed. 



Physiologically, too, the maintenance requirement represents the 

 demand of the basal life processes. The prime necessity of the organ- 

 ism is to maintain itself. It must live before it can grow or propagate 

 its kind, and in the phenomena of maintenance the fundamental 

 processes of nutrition may be studied uncomplicated by the demands 

 of growth, fattening, or reproduction. 



THE FASTING KATABOLISM. 1 



Unlike the operations of a factory, which cease when the power is 

 shut off, the activities of the animal do not stop when food is with- 

 drawn, but continue for a variable length of time at the expense of 

 the materials of the body. It is as if the materials of the factory 

 itself were being cut up and used for fuel under the boilers. Men have 

 fasted voluntarily for 30 days or more without obvious permanent ill 

 effects, and there are records of dogs having survived fasting periods 

 of from 90 to 100 or more days. In the fasting animal at rest the vital 

 activities are reduced, as it were, to their simplest terms, practically 

 only those functions being active which are essential to continued life. 

 The following approximate estimate by Zuntz of the factors of the 

 katabolism of a fasting man may serve to give a general idea of their 

 nature and relative importance. Tne figures show the oxygen con- 

 sumption per minute of the various tissues and its percentage distri- 

 bution : 



1 For references to the literature of the fasting katabolism compare : 

 Magnus Levy. Von Noorden's Pathologie des Stoffwechsels, 2d od., I, 222-225 and 

 310-315. 



Tigerstedt. Nagel's Handbuch der Physiologie des Menschen, I, 375-391. 

 Lusk. The Science of Nutrition. 2d ed., 54—85. 



Benedict. Metabolism in Inanition. Carnegie Institution of Washington, Publication 

 No. 77, II, 3G1-3G4. 



Armsby. Principles of Animal Nutrition, 3d ed., 80-92 and 340-347. 



