1912.J 



The Feeding of Farm Stock. 



903 



cular energy upon the performance of work other than 

 that included under (b) (External Work), this extra task 

 can only be provided for by the supply of correspondingly 

 increased amounts of digestible nutrients. 

 The requirements summarised in (a), (£>), and (c) may be 

 referred to as the " maintenance requirements." A ration 

 which satisfies these requirements without leaving any margin 

 for the productive purposes summarised under (d) may there- 

 fore be described as a ''maintenance ration." It represents 

 the minimum supply of food upon which the animal, when 

 completely at rest, can sustain a normal existence without 

 losing weight. Among animals of the same class it will be 

 roughly proportional to the live-weight of the animal. 



Any food supplied in excess of the maintenance require- 

 ments can be utilised by the animal with varying efficiency 

 for the productive purposes outlined under (d), and may 

 therefore be described as the "production ration," or the pro- 

 ductive part of the total ration. 



It is obviously impossible in the case of young growing 

 animals to draw any such sharp distinction between main- 

 tenance and production, since there can be no "marking 

 time " in the growth of the animal, such as simple maintenance 

 would involve. In the case of full-grown animals, however, 

 it is profitable to keep this distinction in mind in constructing 

 rations; thus the maintenance requirements of a cow remain 

 practically the same whether she yield two gallons or four 

 gallons of milk daily. It is the production requirements that 

 are halved when the milk-flow is halved, not the total require- 

 ments. Similar considerations apply also in the case of 

 working animals. 



The various ingredients (albuminoids, oils, &c.) of foods are 

 not of equal value to the animal for the discharge of the 

 requirements summarised above. There are, indeed, certain 

 purposes (included in (c) and (d)) — viz., purposes which in- 

 volve the production of albuminoids in the body, such as the 

 production of muscular tissue (lean meat), hair, skin, &c, or 

 of the albuminoids present in the various body fluids and 

 secretions — that can only be supported by albuminoids * in 



* There is reason to believe that albuminoids may be partly replaced by " amides," 

 but it is doubtful whether rations entirely free from albuminoids could be entirely 

 satisfactory, even though rich in "amides." 



