3 86 



NUTRITION OF FARM ANIMALS 



Evidently the protein supply was sufficient in the first period to 

 ensure normal growth. The additional supply in the second period, 

 therefore, had no effect on the gain but simply increased the protein 

 katabolism, i.e., the added protein was used as a source of energy for 

 maintenance or for the production of fat. 



On the other hand, a supply of protein notably insufficient to per- 

 mit normal gain may yet show a comparatively high percentage re- 

 tention. Thus the same calf received in an intermediate period only 

 4 kgs. per day of whole milk together with sufficient butter fat and 

 lactose to supply the necessary energy. As compared with the first 

 period only about one-half of the normal gain of protein was secured, 

 yet the percentage retention is but slightly reduced. 



TABLE 85. HIGH PERCENTAGE RETENTION OF NITROGEN ON INSUFFI- 

 CIENT PROTEIN 



469. Influence of deficient energy supply. But not only 

 may a surplus of protein be utilized as a source of energy in the 

 manner just illustrated, but if the energy supply in the feed 

 is inadequate protein may be diverted from growth to serve 

 as fuel material, precisely as in the case of maintenance (412), 

 thus lowering both the observed gain and the percentage re- 

 tention. 



This effect is well illustrated by the following experiment by Fin- 

 gerling upon a calf receiving in the first two periods a limited quan- 

 tity (10 kgs. per day) of whole milk. As the animal grew -older the 

 energy supply became insufficient and protein was diverted to fuel 

 purposes so that the actual gain and the percentage retention both 

 diminished. When, in a third period, one-half of the milk was re- 

 placed by butter fat, the protein supply being kept at nearly the 

 same level by the addition of egg albumin, the actual gain rose nearly 

 to its original level and the percentage retention became even higher 

 than at first on account of the somewhat reduced protein supply. 



