262 NUTRITION OF FARM ANIMALS 



Since comparatively insignificant movements have such a 

 striking effect upon the total katabolism, it is evident that the 

 amount of muscular activity must be an important factor in 

 determining the relative energy requirements of two animals 

 even though their minimum katabolism in a state of absolute 

 rest may be identical. In experiments of any considerable 

 duration on normal animals, it is impossible to avoid more or 

 less expenditure of energy in, this incidental muscular work, 

 while it is often a matter of difficulty to make the different 

 periods of an experiment comparable in this respect. 



349. Standing and lying. Considerable muscular exertion 

 is required during the waking hours to maintain the relative 

 position of the different members of the body. This is es- 

 pecially true of standing. It has been shown that a man or an 

 animal when standing excretes notably more carbon dioxid 

 than when resting or lying down and produces correspondingly 

 more heat. Differences of as much as 25 per cent have been 

 observed in man and of 30 to 40 or more per cent, in cattle. It 

 is evident, then, that if one animal lies down for twelve hours 

 and another for only eight hours during the twenty-four, the 

 former will, other things being equal, require less feed energy 

 for actual maintenance than the latter. 



350. External temperature. Farm animals belong to that 

 general class known as warm blooded, or homoiothermic, animals, 

 whose bodies during health maintain a nearly constant tempera- 

 ture which is higher than that of their usual surroundings. The 

 so-called " animal heat " is being continually generated by the 

 katabolism going on in the body, while on the other hand the 

 animal is continually imparting heat to its surroundings in four 

 principal ways: viz., by conduction, by radiation, by evapora- 

 tion of water, and as the sensible heat of the excreta. 



Since the animal is both producing and losing heat continu- 

 ally, the maintenance of a constant body temperature implies 

 the existence of some regulative mechanism by means of which 

 the production and emission of heat may be adjusted to each 

 other. This adjustment is effected in general in two ways which 

 may be called, respectively, physical and chemical regulation. 



351. Physical regulation of body temperature. Changes 

 in the temperature of its surroundings, in the relative humidity 

 of the air, etc., tend to produce the same effect upon the animal 



