CALCIUM AND PHOSPHORUS Mf THE FEED OF DAIRY COWS. 9 



DISCUSSION OF RESULTS. 



Our, results indicate that the milk yield of the general herd at 

 Beltsville has been reduced by an insufficiency either of calcium or 

 of phosphorus, or of both, in the rations, in spite of the facts that 

 these contained more than the average proportions of both calcium 

 and phosphorus and were fed in the amounts required according to 

 the feeding standards. We think it is still an open question whether 

 calcium or phosphorus has been the element chiefly lacking, and 

 whether the rations could be improved from the standpoint of min- 

 eral nutrition by varying the proportions of the different feeds used. 

 Work aimed to throw light on these problems is now being carried 

 out here. In the meantime, however, it seems worth while to con- 

 sider what the knowledge already at hand indicates ought to be 

 done. 



Table 1 contains the cases where a cow s record after the phosphate 

 feeding is compared with a previous record of her own made after a 

 period on the basal ration. It will be noted that in most of these 

 cases the basal ration was fed before the first calf was born. The 

 results as given in this particular table, therefore, are chiefly evi- 

 dence for the view that the heifers received insufficient calcium or 

 phosphorus in the rations supplied to them before they had their 

 first calves. 



We believe that this was the case, and we shall later discuss the 

 rations supplied to the heifers which had never had calves. But the 

 records for the general herd indicate that, under the Beltsville 

 routine, the animals never recovered from the mineral shortage which 

 made itself evident in the first lactation period. 



The evidence from the records which indicates this may be summed 

 up as follows : In the case of the animals born at Beltsville and kept 

 under the routine treatment there was no tendency for the milk yield 

 to rise after the first lactation period to the extent that it did in the 

 cases of cows 54, 63, 71, and 81, shown in Table 1. The rise as be- 

 tween the first and subsequent lactation periods was approximately 

 that which would be expected from the data collected by Pearl and 

 Patterson (14) and by the Holstein and Guernsey breeding asso- 

 ciations. In the case of animals brought to the farm from other 

 places and kept under the routine treatment, there was frequently a 

 tendency for the milk yield to fall off more rapidly than it should 

 with advancing age, as in the cases of cows 17 and 201, figures 1 and 2. 



As many of the cows which received the alternated rations with 

 phosphate received a basal ration somewhat lower than that fed to 

 the general herd during their dry periods, it is fair to compare the 

 milk yields of these two sets of animals. Cows 49, 54, 71, and 81 may 

 be taken as representing the effects of the phosphate feeding in the 

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