DIGESTION AND ASSIMILATION 173 



bird's body warm; (2) they are burned and produce the energy 

 required by the bird in moving; (3) if the supply of either is greater 

 than that required for heat and energy, the excess gives rise to 

 the laying up of fatty tissues. The principal difference between 

 these two formers of heat and energy lies in the fact that fat has 

 the greater energy value, being rated at two and a fourth times 

 that of carbohydrates. 



Little care need be taken to supply ash for the uses of the adult 

 animal, because the substances which furnish it are usually present 

 in the ordinary ration in sufficient amounts; but the growing birds, 

 especially the maturing pullets, require a greater proportion. Care 

 must be taken to supply for their use an abundance of mineral 

 matter, as it goes toward the formation of the bony framework of 

 the body, and a large, well-developed body is impossible without 

 an adequate frame. Mineral matter can best be supplied to the 

 young birds in the form of wheat bran, which is easily and quickly 

 digested, or by feeding finely ground oyster shells and lime grit. 

 Laying birds require a ration well supplied with ash to provide 

 material for the formation of the shells of their eggs. 



The three principal nutrients, protein, carbohydrates, and fat, 

 are the important ones to consider when buying feeds, and it is 

 well to determine the value of the purchased material by the 

 weight of digestible protein which it contains. 



Water Supply. The prime necessity of an abundant supply of 

 water is too often overlooked, and the matter of cleanliness should 

 not be neglected. Water has four definite functions to perform 

 hi the bird's body: (1) It fills up and distends the tissues, giving 

 them a plump appearance; (2) it aids in digestion by dissolving 

 particles of feed, so that the digestive fluids can act on them more 

 readily; (3) it aids in transporting digested matter and greatly 

 hastens assimilation by stimulating diffusion; (4) it aids greatly 

 in the regulation of body temperature. The need of keeping a 

 supply of fresh, pure water constantly accessible to birds cannot 

 be too strongly emphasized. 



Digestion and Assimilation. Much of the feed of domestic 

 birds is in the form of seeds, whole grains, and the like. Such 

 materials as are hard and lumpy, or are encased in hard, fibrous 

 husks which resist the action of the digestive juices, cannot be 

 immediately available as nourishment; they must be ground and 

 crushed by the digestive organs before they can be used in the body. 

 The natural means provided for this purpose are hereafter described. 



