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 ma}^ 
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 Rept 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. 
