52 Report of Departmext of Animal Husbandry of tub 



The foiogoing figures make it plain that the excess of diges- 

 tible protein in the ration over and above that needed for the 

 milk, rather than a.ny demand for milk secretion, largely deter- 

 mines the extent to which protein suffers destructive changes. 

 In the case of the grade Jersey the daily protein supply was 

 gradually diminished from 1.8 lbs. to .0 lb. and with Cow 12 

 from 2.0 lbs. to 1.0 lbs. The most marked result was to depress 

 the daily protein decomposition from .86 lb. to .40 lb. in one case 

 and from 1.2 lbs. to .00 lb. in the other case. When the food 

 protein was increased to the original quantity the reverse process 

 took place. While the protein utilized for milk secretion was 

 somewhat lessened when the food protein was decreased, tho 

 depression of milk yield was not at all commensurate with the 

 drop in the digested protein. This accommodation of the cow's 

 metabolic process to a diminished protein supply mostly hj a 

 decrease in protein decomposition rather than wholly by depress- 

 ing the milk production, indicates what the writer has previously 

 suggested, that protein exchange outside the formation of the 

 nitrogen compounds of the milk has no constructive function and 

 that so large a quantity of protein as 2.5 lbs. daily for the aver- 

 age cow is justified only on the theory that the balance above 

 what is really utilized in the mi.k and what would be required 

 for maintenance in a non-producing animal acts to stimulate 

 milk secretion rather than to support it. These comments are 

 not to be taken as implying that a liberal supply of protein is not 

 promotive of generous milk secretion. 



A view unsupported by valid evidence, which has been more 

 or less current and has been to some extent accepted in a pop- 

 ular way, is that the fat supply in the food modifies butter fat 

 formation to an important extent. It is already shown in the 

 context that with Cow 10 a large increase in the food fat did not 

 affect the proportion of fat in the milk or the amount secreted. 

 Xo intpiiry was nuide as to whether the constitution of the but- 

 ter fat mixture was in any way affected. 



