MAINTENANCE RATION AND FATTENINGS 437 



Factors which Affect the Maintenance Ration. The size of the 

 maintenance ration is affected by several factors in addition to 

 the vital needs of the animal. 



External Temperature. When the atmosphere has the same 

 temperature 'as the animal body, no heat is required to keep the 

 animal warm. The thermal energy of the food, produced in 

 digestion, will maintain the animal heat for a few degrees below 

 33, which will vary according to the character of the food. At 

 lower temperatures, food must be oxidized to keep the animal 

 warm. The amount of food so required will depend upon the 

 temperature, and other factors. For example, Rubner 1 found 

 the heat given off by a starving dog, is measured directly in a 

 calorimeter, to be as follows : 



Temperature Heat evolved 



Degrees C. Calories 



7.6 86.4 



15-0 63.0 



20.O 56.0 



25-0 54-0 



30.0 56.0 



35-0 68.5 



About 65 per cent, more energy was used at 7.6 C. than at 

 25. At 35 the elimination of heat is increased, probably owing 

 to disturbances due to the high temperature. 



Feeding standards are based on a temperature of 15 to 20 C. 

 At higher temperatures, less feed will be required, at lower tem- 

 peratures, more. Since small individuals have a proportionally 

 larger body surface than the large animals, they give off more 

 heat, and so require more food. For example, it is estimated 

 that a grown steer weighing 300 pounds would require per 100 

 pounds weight, food of 0.19 pounds fat value, while a steer of 

 800 pounds, requires per 100 pounds weight, food of 0.14 pounds 

 fat value, or one-fourth less, weight for weight. 



The Condition of the Animal. The fatter the animal, the 

 more food it requires for maintenance. The increased food 

 required is not in proportion to the gain in weight, but the pro- 

 1 Gesetz d. Energieverbrauch, 1902, p. 105. 



