454 NUTRITION OF FARM ANIMALS 



the evolution of relatively large amounts of heat, especially 

 in the ruminants, and that the effect of this internal produc- 

 tion of heat is virtually to lower the critical temperature as com- 

 pared with that of the fasting animal. In other words, there is 

 for each animal and for each ration a certain temperature above 

 which the heat produced becomes in part an excretum, to be 

 gotten rid of by radiation and evaporation. 



It appears likely that a certain excess of heat production over 

 that absolutely required to maintain the body temperature is 

 advantageous, both as promoting the comfort of the animal and 

 especially as affording a margin in case of temporary fluctuations 

 of temperature. On the other hand, both our own personal sen- 

 sations and the observations of practical stock feeders show that 

 an unnecessarily high temperature is debilitating, affecting both 

 appetite and general health. In practice, then, it is desirable to 

 keep the thermal surroundings of the animal within the range 

 above indicated somewhat above the critical point but not 

 so much so as to affect the appetite and thrift. It is evident 

 that the limits of this range may vary widely with the kind of 

 animal and with the amount of the ration. 



537. Amount of ration. The influence of this factor upon 

 the requirements for protection from cold is clearly indicated 

 by what has already been said. The heavier the ration, other 

 things being equal, the more heat will be evolved during its 

 digestion and conversion into tissue. Mature animals on full 

 feed thus have at their disposal a large amount of surplus heat 

 and naturally can thrive under conditions of exposure which 

 might be seriously detrimental to young, growing animals on 

 relatively light rations. Thus one of Kellner's experiments on 

 a fattening ox gave the following results : 



TABLE 118. EXCESS HEAT PRODUCTION IN FATTENING 



Metabolizable energy of ration 26,600 Cals. 



Energy stored as gain 5>9 2 Cals. 



Energy evolved as heat 20,740 Cals. 



Computed maintenance requirement .... 15,060 Cals. 



Excess of heat 5, 680 Cals. 



Excess over maintenance 37-7% 



538. Age and weight of animals. The internal work of 

 like animals of different sizes, under like conditions, appears to 



