Nutrition Studies. 73 



2. Maintenance. 



96. Maintenance rations for mature animals. The maintenance 

 ration must furnish sufficient nutrients to cover the requirements 

 of the body for heat, to furnish the energy expended in the work of 

 the heart, lungs, digestive and other internal organs, and in the 

 slight movements of the body always occurring, as well as to fur- 

 nish material for repairs. The heat requirements of the resting 

 animal are ordinarily in excess of the energy requirements for in- 

 ternal work. Hence the maintenance ration of farm animals, ex- 

 cept the pig, may consist largely of roughages, such as hay and 

 straw, which furnish much heat but, being of rather low availa- 

 bility, do not yield much net energy. (70) The supply of protein 

 must suffice to replace the small necessary daily loss of nitrogenous 

 body tissues, and also to furnish material for the growth of the 

 nitrogenous hair, hoofs, wool, etc. As this demand for protein is 

 relatively small, the ration may have a wide nutritive ratio, nine- 

 tenths or more of the nutrients consisting of carbohydrates used 

 solely as fuel. The most economical maintenance ration provides 

 no excess of protein, for such excess causes a greater waste of pro- 

 tein from the body. There is considerable variation in the main- 

 tenance requirements of different individuals of the same size and 

 species kept under the same conditions, due to differences in tem- 

 perament. Restlessness causes greater muscular activity, and 

 thereby increases the demand for food fuel. A quiet animal re- 

 quires less food for maintenance than a nervous, active one. Dur- 

 ing experiments with a horse in a respiration chamber, Zuntz and 

 Hagemann 1 found that the presence of flies caused the animal to 

 give off over 10 per ct. more carbonic acid gas than normally, which 

 means that this much more food fuel was burned. Work is ex- 

 pended in merely maintaining the position of the body, especially 

 when the animal is standing. Armsby 2 found that the ox in the 

 respiration chamber produced over 30 per ct. more heat when 

 standing than when lying down. The physical condition of the 

 animal also affects the maintenance requirement. Kellner 3 shows 

 that the ox in good condition, especially when fat, requires a larger 

 ration for maintenance than a lean one of the same body surface. 



Maintenance requirements vary with the size and weight of the 

 animal. The loss of heat and energy from the body is not propor- 



1 Landw. Jahrb., 23, 1894, p. 161. 



2 Proe. Soc. Prom. Agr. Sci., 1902. 



s Landw. Vers. Stat., 50, 1898, 245 ; 53, 1900, 14. 



