ENERGY VALUES OP RATIONS EOR FARM ANIMALS. 5 



THE DEMAND FOR REPAIR MATERIAL. 



The repair material for any machine must be of the same kind of 

 which the machine is made. We have just seen that the machinery of 

 the body is composed of protein, ash, and water. These, then, are 

 the materials which must be supplied to keep it in repair. 



Water, of course, is or should be abundantly supplied in the drink 

 and scarcely need be considered in a discussion of rations. 



Ash. — The ash supply has received less attention in the past than 

 its importance deserves. In the ordinary operation of the bodily ma- 

 chinery its ash ingredients are being continually excreted and the 

 feed must supply ash sufficient in amount and of the right kinds to 

 make good the loss, while the growing animal needs an additional 

 supply for building up its new tissues. Fortunately, normally con- 

 stituted rations appear rarely to be deficient in ash. Usually it is 

 only when large amounts of certain by-product feeds are used or 

 when there is a misrelation between grain and coarse fodder that 

 special attention needs to be given to the ash supply. 



Protein. — The protein supply, on the other hand, calls for careful 

 consideration. Protein is the characteristic ingredient of the animal 

 mechanism and is broken down, and destroyed in its operation at a 

 fairly regular rate. Moreover, since the bodily machinery is running 

 all the time, whether any external work is done or not, this loss is 

 continually going on. 



The body differs from a machine in being self-repairing, but it 

 can not manufacture protein for repair purposes out of the carbo- 

 hydrates and fats of its feed any more than it is possible to make 

 repairs for an automobile out of the gasoline which supplies the 

 power. For its protein the body is absolutely dependent on the 

 protein of the feed. This protein is needed for two purposes. 



First. It is required for repair purposes in the strict sense; i. e., 

 for making good the wear and tear of the bodily machinery. The 

 amount needed for this purpose is comparatively small, and is no 

 greater under normal conditions when the animal is doing work than 

 when it is not. Like a good engine, the body makes relatively small 

 demands for repair material and requires chiefly fuel. 



Second. Protein as well as ash is needed in the growing, pregnant, 

 or milking animal to furnish the material for enlarging the working 

 machinery of the body of the animal itself or of its young. The 

 amount of protein required for this purpose is just so much in addi- 

 tion to that needed for repair purposes simply, and hence the feed of 

 these animals must contain a more liberal supply of this ingredient. 

 This is important physiologically to secure proper nutrition of the 

 young and economically because the growth or milk produced is the 

 principal object of the feeder. 



