GROWTH AND FATTENING 77 



can occur in mature animals is in the growth of the nitrogenous hair 

 and hoofs, and in the small amount of protein and mineral matter in the 

 fatty tissues. 



We have seen that maintenance rations may consist chiefly of rough- 

 age, which furnishes little net energy. On the other hand, for thrifty 

 growth, the ration must be more concentrated (that is, must furnish 

 more net energy) to provide for the energy stored in the growing tissues 

 of the body in the form of protein and fat. Furthermore, the rations for 

 growing animals must contain adequate supplies of vitamines, as dis- 

 cussed later in this chapter. (120) 



114. Utilization of food in youth. It is a well known fact that young 

 animals make much more rapid gains, considering their size, than those 

 made by mature animals, even when fattening. For example, an un- 

 weaned calf may make gains of 2 to 3 Ibs. daily for each 100 Ibs. of 

 body weight, while a daily gain of 0.3 to 0.4 Ib. per 100 Ibs. of body 

 weight is large for the mature fattening ox. 



As we shall see later, mature animals can store much fat in their 

 bodies, but can make no material gains in protein and mineral matter. 

 On the other hand, young animals can retain and build into their 

 protein tissues and skeleton a large part of the protein and mineral 

 matter in their rations. For instance, in respiration studies with a 

 calf 2 to 3 weeks old, Soxhlet* found a storage in the body of 72.6 per ct. 

 of the protein, 96.6 per ct. of the lime, and 72.6 per ct. of the phos- 

 phorus fed in the milk. Weiske 5 found that even when 5 months old, 

 lambs stored 22 per ct. of all the protein digested from their food. 

 While a calf 8 days old will store nearly 0.40 Ib. of protein per 100 Ibs. 

 body weight, the rate of storage of protein rapidly falls. At a month 

 of age it will store only about 0.28 Ib. per 100 Ibs. body weight; at 2 

 months, about 0.16 Ib. ; at 6 months, about 0.08 Ib. and at 10 months, 

 only about 0.05 Ib. 6 These data show that the quantity of protein built 

 up into body tissues steadily diminishes as maturity approaches. 



Numerous practical feeding trials reviewed in Part III of this book 

 show that young animals require considerably less feed for 100 Ibs. of 

 gain in body weight than those which are older. Because of this, 

 young animals have a marked economic superiority in the production 

 of meat. There are several reasons for the more rapid gains and the 

 more economical meat production of young animals. Their gains are 

 much more watery than those of more mature animals, and also con- 

 tain more protein and much less fat, which has a much higher heat 

 value than protein. Much more net energy is therefore required to 

 make a pound of gain on a mature fattening animal than on one which 

 is young and growing. Furthermore, the food consumed by young 

 animals is ordinarily lower in fiber, and hence more digestible and 



4 Ber. landw. chem. Vers. Stat., Wien., 1878, p. 101. 



"Landw. Jahrb., 9, 1880, p. 205. 



Armsby, Nutrition of Farm Animals, pp. 376-7. 



