THE NUTRIENTS AND DIGESTION 305 



when used for food, is one of the ultimate objects of poultry 

 production, and in the case of turkeys and most waterfowl 

 is the primary object. The development of the vital organs 

 is necessary to the maintenance of life itself, while the repro- 

 ductive organs are responsible, not only for the perpetuation 

 of the race, but, in the case of the hen, for the manufacture 

 of the primary product. 



Growth is possible only when there is some source of supply 

 from which bone and protein tissue may be drawn. This 

 source can only be the food that is fed in excess of that needed 

 for the bare maintenance of life. 



Reproduction. — ^When growth is complete, or is nearing 

 completion, reproduction usually occurs. This is a necessary 

 process of production, not only from the stand-point of the 

 perpetuation of the race, as in all species, but, in the case of 

 the hen, because the egg, representing one stage in the repro- 

 ductive cycle, is so highly prized for human food as to have 

 a great commercial value. The whole philosophy of egg 

 production is bound up in the effort to induce abundant 

 reproduction. 



Just as growth is possible when the material out of which 

 growth is made is furnished in excess of that necessary to 

 merely maintain life, so reproduction can only occur when an 

 excess of food is furnished. While generous reproduction 

 depends on several conditions, it cannot be accomplished at 

 all without material out of Vhicn to form the potential new 

 creature, and which is furnished only in the form of food. 



Fattening. — In all birds, and especially in those that have 

 ceased to grow or reproduce, some of the food consumed 

 above that necessary for maintenance is stored up in the 

 body as a reserve in case the regular supply of food fails. 

 This surplus is stored in the form of fat, and increases not 

 only the quantity but the quality of poultry flesh. 



THE NUTRIENTS. 



Every constituent of the feed that can yield heat or energy 

 or can serve for the production of body tissue is called a 

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