FOOD REQUIREMENTS 371 



computing rations to allow a margin of safety in fixing the 

 nutritive ratio. 



2. Rations. 



Feeding tables are contained in text-books on animal 

 nutrition. Owing to the number of different kinds of 

 animals and different kinds of production aimed at in feeding, 

 these tables are somewhat extended. It is only necessary 

 here to indicate the physiological principles on which feeding 

 standards should be based. 



In arranging rations, the chief consideration is that 

 available energy and material will be supplied in sufficient 

 amounts to yield the desired products, e.g. work, milk, or 

 increased weight. It is also usually necessary to arrange by 

 a combination of different feeding stuffs that the total bulk 

 will be suitable for the animal. In practice, other considera- 

 tions such as relative costs, manurial values (p. 380), and 

 the labour involved in preparing the food, are taken into 

 account in deciding what feeding stuff's and what combinations 

 and proportions of these are most economical. 



1. Maintenance. — A maintenance ration is one that supplies 

 just sufficient energy and protein to sustain life without pro- 

 duction and without either gain or loss of tissue. This 

 ration is the commercial base line, since it is only what the 

 animal assimilates beyond its maintenance requirement that 

 can be transformed to a marketable product. 



The ration must cover the basal metabolism fp. 264) 

 plus the increased metabolism due to the consumption of the 

 food (p. 272). If the environment be below the critical 

 temperature (p. 271), a further addition is necessary for 

 heat production to maintain the body temperature. 



A horse of 1000 lbs. weight housed comfortably and doing 

 no work requires a daily ration the digestible nutrients of 

 which yield about 5 kilos protein and 15,000 Calories. 



2. Growth — (1) Material. — In the growing animal there is 

 formation of new tissue and bone. The food therefore must 

 be rich in protein and ash. The rate of growth diminishes 

 from birth onward, and, therefore, the younger the animal the 

 higher is the proportion of protein and ash required. Experi- 



