MILK PRODUCTION 



489 



just as is the case with a surplus supplied to a young animal, or 

 for that matter to a mature animal. Feed protein is substan- 

 tially a supply of material and not a cause of production. 



This is strikingly illustrated in experiments by Jordan 1 in which 

 the protein supply of two cows, beginning with a liberal amount, was 

 gradually diminished to about one-half and then gradually increased 

 again to the original quantity. The following table shows the aver- 

 age nitrogen balances of Cow No. 12 of the second series of experi- 

 ments, the daily results being grouped into periods as indicated. 



TABLE 130. AVERAGE DAILY NITROGEN BALANCE OF Cows 



The yields decreased in quite a normal way with the advance in 

 lactation, the yield of protein, like that of total milk solids, diminish- 

 ing, while the percentage of protein in the latter remained about the 

 same. On the low protein rations of the middle periods there seems 

 to have been some falling off in the amount of milk protein produced 

 in comparison with what might have been expected on an unchanged 

 ration, but the difference is small except in one or two periods in which 

 the protein supply reached the lowest limit. Aside from this, the 

 principal effect of the variations in the amount of digestible protein 

 supplied was to increase or diminish the amount of nitrogen excreted 

 in the urine, which, as the table clearly shows, rose and fell with the 

 supply of nitrogen in the food. 



586. Estimates of utilization of protein. In attempting 

 to reach conclusions regarding the utilization of feed protein 

 for the production of milk protein, then, it is evidently necessary 

 to avoid an excess of protein in the ration, since such an excess 



N. Y. (Geneva) Expt. Sta., Buls. 132 (1897) and 197 (1901). 



