126 THE CHEMISTRY OF CATTLE FEEDING 



radiation is proportional to the difference between the tempe- 

 rature of the animal's body and that of the atmosphere to which 

 it is exposed. For example, when the temperature is down to 

 o C., the animal would lose twice as much heat in a given time 

 as it would when the temperature is up to 20 C., because the 

 difference, as compared with the temperature of the animal's 

 body (40 C.), would be twice as great. There are, however, 

 many other points to be taken into account, such as the con- 

 dition of the animal's coat due to clipping, etc. ; the effect 

 of high winds which rapidly carry off the heat ; warming 

 and evaporation of water which falls upon the skin in wet 

 weather, etc. The effects of all these variable conditions 

 cannot be reduced to a formula ; but they may be summed 

 up in the statement that exposure involves greater loss of 

 heat, and more food must be consumed to maintain the tempe- 

 rature of the body. If the available energy of the food is not 

 sufficient to maintain the temperature, the tissues of the body 

 are oxidised, and the animal loses weight. Conversely, a 

 considerable saving of food may be effected by shelter and 

 warmth. 



Large animals require more food than small ones. An 

 ox, for example, eats much more than a sheep or a pig in a 

 given time. The larger animals evaporate more water, and 

 lose more heat by radiation, than the smaller ones. The 

 amount of food required, however, is not directly proportional 

 to the size as measured by mass. An ox of 1600 Ibs. live 

 weight does not require twice as much food as one of 800 Ibs. 

 Under given conditions, the loss of heat by radiation is pro- 

 portional to the extent of body surface exposed, and the 

 surface does not vary directly as the mass (live weight). 1 



1 The bodies of farm animals, apart from the head and limbs, are 

 approximately cylindrical. In the case of oxen, the length of the trunk 

 or barrel is about i times the diameter. The relation between surface 

 and mass may, therefore, be illustrated by reference to the properties 

 of a cylinder of water of similar dimensions. In such a cylinder, the 

 ratio of surface to volume is inversely as the diameter, and the mass of 

 water in it is proportional to the volume. In the units of the metric 

 system (grams and cubic centimetres) the volume and mass of water 

 are expressed by the same numbers. Thus it is found that when the mass 



