396 NUTRITION OF FARM ANIMALS 



hibited by the mature animal and at any rate to be practically 

 proportional to it. This would mean, of course, that the net 

 energy values of feeding stuffs for maintenance and fattening 

 might be used also to measure at least their relative if not their 

 absolute net energy values for growing animals. 



The determination of the validity of this provisional con- 

 clusion offers an interesting and profitable field for investigation. 



3. THE FEED REQUIREMENTS FOR GROWTH 



478. Contrast with fattening. la the case of fattening 

 animals the conception of the feed requirement, particularly as 

 regards energy, is somewhat artificial, since the extent of the 

 fattening depends, within the limits of the animal's capacity, 

 largely upon the amount of feed supplied. Growth, on the 

 other hand, unless the feed fails to supply the necessary materials 

 and thus becomes a limiting factor, goes on at a rate substan- 

 tially determined by other conditions, the most obvious of 

 which are the species, individuality and age of the animal. 

 Indeed, it may be said that, within normal limits, the capacity 

 for growth determines the feed consumption rather than the 

 reverse. Heavy feeding may cause fattening but it does not 

 appear, at least in the case of the higher animals, to materially 

 accelerate growth, although Eckles 1 observed the growth of 

 dairy calves to be somewhat more rapid upon heavy as com- 

 pared with scant rations. In growth, therefore, as in mainte- 

 nance, there is a real requirement to be satisfied, its measure be- 

 ing the amount and character of th6 increase which the young 

 animal is capable of making under normal conditions. 



Mention has been made (372) of the interesting results of experi- 

 ments by Waters 2 upon growth under adverse conditions, while 

 Osborne and Mendel 3 have shown that growth which has been sus- 

 pended for a time because of inadequate feed supply may be resumed 

 when this deficiency is made good (deferred growth). Neither of 

 these possibilities, however, invalidates the statement just made that 

 the continued maintenance of a normal rate of growth requires a 

 definite supply of matter and energy. 



1 Mo. Expt. Sta., Bui. 135, 1915. 



2 Soc. Prom. Agr. Science, Proc. 2gih Annual Meeting, 1908, p. 71. 



3 Jour. Biol. Chem., 18 (1914), 195; 23 (1915), 439; Amer. Jour. Physiol., 40 

 (1916), 16. 



