CALCIUM AND PHOSPHORUS IN THE FEED OF DAIRY COWS. 5 



though they may get a little pasture in addition. 4 Under this treat- 

 ment the milk yield may be reduced, after a few years, to less than 

 half the optimum ; and when it has been so reduced it may be very 

 greatly increased by liberal feeding during a 2-months' dry period. 



A point of great interest to be noted in the history of cow 201 

 is the length of time which it took for the full effect of the routine 

 method of feeding to become apparent. The milk yield did not 

 reach its lowest point until she had been on the farm for four years. 



NATURE OF THE DEFICIENCY IN THE ROUTINE RATIONS FED 

 AT BELTSVILLE. 



It is probable that the rations fed at Beltsville were not deficient 

 in a general sense, but deficient only in one or a few particular con- 

 stituents necessary for milk secretion. The cows were kept in good 

 general condition, which seems to indicate that they received enough 

 of the energy-yielding portion of the ration. The recent very inter- 

 esting work of Forbes (5) indicates that cows milking liberally may 

 often receive insufficient calcium and phosphorus in their rations. 

 The experiments reported in this bulletin were directed toward 

 throwing more light on that question. 



There is no doubt that a cow's milk yield may be markedly in- 

 fluenced by the nutriment which she receives during 6 or 8 weeks be- 

 fore her calf is born. The experiments to be reported have, there- 

 fore, been confined to the influence of the ration fed during this 

 period on the subsequent milk yield; and, for the reasons that 

 follow, the phosphorus fed during the dry period has been varied 

 rather than the calcium. 



The results of certain metabolism experiments in which the cal- 

 cium and phosphorus balances have been followed — particularly 

 those of Forbes (5) and Hart (8) — seem to show that calcium and 

 phosphorus metabolism are largely independent of each other. In 

 these experiments, however, the calcium and phosphorus balances 

 were not followed for more than 20 days successively. There is no 

 reason to doubt the figures that have actually been obtained, and it 

 is very likely that a cow may lose 200 or 300 grams of calcium while 

 remaining in phosphorus equilibrium. But it is doubtful whether 

 the metabolic independence of the two elements ever goes much 

 further than this. In a recently published article this question was 

 discussed in some detail, and it has been pointed out that the weight 

 of evidence obtained from carcass analyses is strongly against the 

 view either that the ratio of calcium to phosphorus in bone is subject 



4 Our evidence shows only that cows are not Kept up to their optimum milk yield when 

 fed the protein and total nutriment required by the standards in the form of the 

 amounts of grain, hay, and silage used on the Beltsville farm. The reader must judge 

 for himself how closely this method of feeding approaches what is typical throughout 

 the country. 



