74 



Feeds and Feeding. 



tional to the size or weight, but rather to the body surface. This 

 is shown by Rubner, 1 who determined the quantity of heat given 

 off daily by fasting dogs of different sizes but in the same bodily 

 condition, as reported in the following table : 



Heat given off ~by fasting dogs of different sizes. 



It is shown that while the heat evolved daily per square meter 

 of body surface remained nearly constant, the larger the animal 

 the smaller was the daily loss per kilo of body weight. This is be- 

 cause large bodies have less surface in proportion to their weight 

 than small ones, and the loss of heat from the body is largely de- 

 termined by its relative surface. Hence maintenance rations should 

 be proportional to the surface of the body rather than its weight. 

 Since it is difficult to actually measure the surface of an animal's 

 body, the maintenance ration for animals of different sizes may be 

 computed by the well-known geometrical law that the surfaces of 

 solids are proportional to the squares of the cube roots of their 

 weights. The protein requirement for maintenance depends not 

 upon the surface of the body of the animal, but directly upon its 

 weight. 2 



The temperature of the animal's surroundings also influences the 

 amount of food required for maintenance, tho not to the degree 

 often supposed. Since with the mature animal at rest and on main- 

 tenance the fuel value of all digested food is finally liberated as 

 heat, the heat furnished by the maintenance ration is usually amply 

 sufficient to maintain the body temperature. At an unusually low 

 temperature the animal on a mere maintenance diet may require 

 additional food to keep the body warm. 



97. Minimum protein requirement. In view of the high cost and 

 relative scarcity of crude protein in feeding stuffs, it is desirable 

 to know the minimum requirement of crude protein by farm ani- 



1 Ztschr. Biol., 19, 1883, p. 535, 



2 Kellner, Ernahr. landw. Nutztiere, 1907, p. 410. 



