772 
Journal of Agricultural Research 
Vol. XXXI, No. 8 
two reasons for this: (1) the important part played by these elements 
in the animal system, and (2) rations are more likely to be deficient 
in them than in any other mineral element. 
.Forbes (4, 5, 6 , 8 , 9 ,) and his coworkers at the Ohio Agricultural 
Experiment Station conducted a very elaborate and comprehensive 
series of metabolism experiments with cows in different stages of 
lactation. They found that high-producing cows in the earlier 
stages of lactation, even when fed on rations rich in calcium and 
phosphorus, invariably showed negative calcium balances and 
generally had negative phosphorus balances. This negative balance 
persisted until the later stages of lactation. When the milk flow had 
dropped to about 10 pounds daily the animals began to show positive 
balances of calcium and phosphorus, and from that time until calving 
the intake of these elements was greater than their rate of excretion. 
In other words, the losses of early and middle lactation were made good 
by storage during the later stages of lactation and in the dry period. 
Forbes considers this tendency on the part of milking cows to excrete 
their body reserves of calcium and phosphorus to be due to the 
intensification by breeding of the function of milk secretion to a point 
which is beyond the animal's ability to assimilate these elements 
from her feed. 
As a result of his studies, Forbes recommends that cows be fed a 
ration naturally rich in calcium and phosphorus, i. e., one containing 
legume hay as a roughage, which is nothing more than a matter oi 
good dairy practice. In addition he recommends a diw period of 
six to eight weeks, during which time the cow is to be fed liberally 
on a mineral-rich ration in order that she may make good the depleted 
mineral reserves of her body. He has also studied the possibility of 
supplying calcium in the form of mineral supplements, and his 
conclusion is that “it is not clear that supplemental calcium is 
utilized," although he suggests “for practical experimental pur¬ 
poses, the feeding of calcium phosphate in the form of steamed 
bone." 
Forbes (5, 7) also conducted extensive experiments with swine op 
the value of mineral supplements in the ration. He found that pigs 
supplied with either precipitated calcium carbonate or special steamed 
bone had relatively dense and strong bones; that in pigs fed rock 
phosphate as a supplement the bones had about the same character¬ 
istics as those fed on a ration containing no mineral supplement, viz., 
relatively low breaking strength and density; that the hardest bones 
contained the highest proportions of calcium and total ash, while the 
softest bones contained the highest proportions of phosphorus and 
magnesium and relatively little calcium. He considered that the 
amounts of calcium, magnesium, and phosphorus in the bone are 
susceptible of much greater modification through the composition 
of the food than are their relative proportions. Special steamed bone 
proved to be the most satisfactory mineral supplement for swine of 
any he investigated. 
Another prominent group of investigators in this field has been 
Hart and his colleagues at the Wisconsin Agricultural Experiment 
Station. Their earlier work was principally with swine. They 
demonstrated (18) that hogs arc very sensitive to low ash content 
in their rations, that they can utilize inorganic phosphate to advan¬ 
tage, and that organic phosphorus (e. g. phytin) is no better than 
tricalcic phosphate for supplying the animal's needs for phosphorus. 
