MAINTENANCE OF FARM ANIMALS 59 



the air temperature falls again these processes are reversed. In addition 

 to these means of controlling the loss of heat, the clothing of man, and 

 the hair, wool, feathers, or thick skin of animals check and control its 

 loss from the body. 



The relative importance of the various channels thru which heat is 

 lost depends upon various conditions, including the species of animal. 

 In humans, 2 about 73 per ct. is lost by the radiation and conduction 

 from the skin, 14 per ct. by the evaporation of water from the skin, 7 

 per ct. by vaporizing water from the lungs, 4 per ct. by warming the 

 air breathed out, and 2 per ct. in the feces and urine. 



When the temperature of the air falls below a certain point, another 

 means of heat regulation must be brought into action ; i. e., an increase 

 in the rate at which heat is produced in the body. This is similar to 

 increasing the fire in a room, if it is still too cold after the windows are 

 all closed. This greater heat production is brought about by increasing 

 the oxidations of nutrients in the tissues of the body. This may be 

 accomplished partly more or less voluntarily, but may also be entirely 

 involuntary. On cold days, for example, animals eat more heartily and 

 take more exercise than in warm weather, both of which result in the 

 formation of more heat. A low external temperature also causes an 

 involuntary stimulation of the oxidations going on in the tissues, which 

 may even become visible in the shivering of the chilled animal, that is 

 the outward manifestation of increased muscular contractions, started 

 solely to produce more heat. 



Because the loss of heat is largely controlled by the clothing he wears, 

 man has, in some measure, lost his power of heat regulation. With many 

 of the warm-blooded animals, however, this power is highly developed. 



90. Heat and energy required for maintenance. Experiments have 

 shown that with a mature animal being maintained at rest in the stall 

 the requirement for fuel to keep up the body temperature ordinarily 

 greatly exceeds the amount of net energy needed for the internal work 

 of the body organs. As will be shown later (448), Zuntz found that to 

 maintain the horse at rest only one-third of the total energy of the ration 

 need be supplied in the form of net energy, the remainder serving simply 

 as body fuel. Hence, except for the pig, the maintenance rations of 

 farm animals may consist largely of roughages, such as hay and straw, 

 which furnish abundant heat, but do not yield much net energy. (78-80) 

 Since the ration must furnish at least a minimum amount of net energy, 

 animals cannot be maintained on such feeds as wheat straw alone, which 

 furnish no net energy to the horse and but little to the ruminant. 



Due to differences in temperament, there is considerable variation in 

 the maintenance requirements of different individuals of the same size 

 and species, kept under the same conditions. As restlessness causes 

 greater muscular activity and thereby uses up more body fuel, a quiet 

 animal requires less food for maintenance than a nervous, active one. 



2 Howell, Text Book of Physiology, 1907, p. 861. 



