SIMPLIFIED TECHNIQUE AND APPARATUS FOR 

 MEASURING ENERGY REQUIREMENTS 



OF CATTLE 



By Ernest G. Ritzman, Research Professor in Animal Nutrition, 

 New Hampshire Agricultural Experiment Station, and Francis G. 

 Benedict, Director, Nutrition Laboratory, Carnegie Institution of 

 Washington 



INTRODUCTION 



The development of the Laboratory for Animal Nutrition at the New 

 Hampshire Agricultural Experiment Station came about as an 

 essential part of an investigation on the physiological effects of under- 

 nutrition on cattle. This work was begun in 1918 and has since been 

 carried on co-operatively with the Nutrition Laboratory of the Carnegie 

 Institution of Washington. The co-operation has been of a singularly 

 satisfactory nature because of the distinct contribution each institution 

 has been able to make to the development of the laboratory 

 and thus to its function as a whole. The activities of this laboratoiy 

 lie primarily in the field of energy metabolism. Its general aim has so far 

 been twofold: (1) the investigation of the physiological requirements of 

 farm live stock for net energy, and (2) the design of equipment and tech- 

 nique to simplify and improve methods for the study of energy trans- 

 formations in farm live stock. 



Since Lavoisier demonstrated the fundamental relationship between 

 oxygen consumption, carbon-dioxide production, and heat production, 

 further research has conclusively established the relative constancy of this 

 phenomenon under the great variety of conditions in which heat is pro- 

 duced. The applicability of this knowledge in measuring in terms of a 

 single unit the heat produced has revolutionized the potentialities of 

 measuring the energy requirements of animal life, and of measuring the 

 extent to which different feed stuffs may supply these requirements. 



The complicated and time-consuming measurements of heat production 

 by direct calorimetiy are now no longer necessary, either with humans 

 or with animals, but the energy transformations may be determined indi- 

 rectly by measurement of the respiratory exchange. Numerous de- 

 scriptions have been put on record stating the object of indirect calorime- 

 tr}' and explaining the principle on which it depends. A brief summary of 

 the principles involved may, however, be given here. 



Energy is the activating force which gives motion, heat, and thus active 

 life to the otherwise inert body protoplasm. Energy is produced by 

 oxidation, which in the human or animal body is in essence a decomposi- 

 tion of organic substances containing primarity the elements carbon, 

 hydrogen, and oxygen in various combinations, but often including addi- 

 tional elements, such as nitrogen in the body cells. In this oxidation, 

 which is either of body tissue or of food material, a definite amount of 

 additional oxygen must be supplied by the outside air. This is delivered 

 through the lungs to the blood stream and thus to the mass of body cells. 



