THE FATTENING OF MATURE ANIMALS 363 



contained nearly 92 per cent of fat and to have had an energy content 

 of 4002 Cals. per pound. The same investigators also obtained en- 

 tirely similar results in the fattening experiments on lambs cited in 

 Chapter XI (458) although naturally the proportions of water and 

 protein in the increase were greater than in the case of the mature 

 sheep. 



During the earlier stages of fattening, especially with thin 

 animals, the storage of fat is accompanied by a considerable 

 gain of water and by more or less increase in body protein. As 

 the fattening progresses, however, the gain comes to consist 

 to an increasing extent of fat accompanied by very little protein 

 and a relatively small percentage of water. The energy 

 content of a unit of gain in live weight, therefore, in the later 

 stages of fattening is materially greater than in the earlier 

 stages of the process. Evidently, then, more net energy will 

 be required in a fattening ration to produce a pound of increase 

 in live weight toward the close of the fattening process than at 

 its beginning, a fact which is entirely in harmony with the ex- 

 perience of feeders that gains become increasingly expensive as 

 the animals become fatter. 



So far as definite conclusions are warranted from the rather 

 scanty data available, it would seem that in the earlier stages 

 of fattening a ration supplying (in addition to maintenance) 

 about 2.5 Therms of net energy would be sufficient to support 

 a gain of a pound of live weight, while in the later stages the 

 requirement may rise to 4.0 Therms or perhaps even more. 



Protein requirements for fattening 



453. Protein unnecessary for fat production. It was 

 shown in Chapter V (247-249) that body fat, especially in the 

 case of farm animals, is derived chiefly from the non-nitrog- 

 enous nutrients of the feed, protein playing but a subordinate 

 role in its production, and Kellner has shown (769) that the 

 proportion of the energy of protein which can be stored up by 

 mature fattening animals is distinctly less than the correspond- 

 ing percentage for the non-nitrogenous nutrients. So far as 

 simple fat production is concerned, therefore, it would appear 

 that a surplus of protein over that required for maintenance 

 would be unnecessary and possibly disadvantageous on account 



