Oct. 15,1925 Gdlcium Phosphate as Supplement to Dairy Ration 773 
Following up the investigation, they concluded (14) that calcium is 
the mineral element most likely to be deficient in ordinary rations 
and that swine should receive some form of supplemental calcium 
in addition to their grain ration. 
Their work with cows on mineral metabolism has been the natural 
outgrowth of a most interesting series of experiments in which it 
was strikingly demonstrated that rations from different sources have 
a decidedly different biological value, regardless of how similar they 
may be with respect to digestible protein and net energy. In the 
ease of rations restricted to the oat-plant, reproduction in cows was 
a failure, the calves being born either prematurely dead, or weak (16). 
When calcium salts, either carbonate, phosphate, or acetate, were 
added to the ration, a marked improvement in the reproductive 
function was noted. 
Their more recent work has consisted of a series of mineral metab¬ 
olism experiments with goats and cows, attention being centered on 
the assimilation of calcium (17). Their conclusion, as a result of 
four separate investigations, is that calcium assimilation is facilitated 
by the presence in the ration of an unidentified accessory substance 
which is present in green roughage and in dry roughage which has 
been carefully cured without exposure to direct sunlight, but not 
in dry roughage as ordinarily cured. They consider as a result of 
their work with goats (17) and dogs (28) that cod-liver oil contains 
the same substance. Their evidence on this latter point is strength¬ 
ened by some work of McCollum et al. (21) who have demonstrated 
the existence of a fourth vitamin in cod-liver oil and other fats 
distinct from vitamin A and having to do with the metabolism of 
calcium. 
Hart and his coworkers (17) also conclude that the ordinary 
grasses, even in their green state, do not furnish sufficient calcium 
to meet the needs of milking cows. The calcium must be supplied 
either in legume hay or as a mineral supplement, with the additional 
safeguard of some medium which carries the unidentified accessory 
substance essential to optimum utilization of the calcium. 
Meigs, (22) of the United States Department of Agriculture, has 
also conducted a series of investigations on the subject of mineral 
matter for cows. His principal conclusion is essentially the same as 
that of Forbes, viz, that cows should be given a two-months’ dry 
period, during which time they should be liberally fed on a ration 
rich in calcium and phosphorus. He noted a phenomenal increase 
in milk yield when cows were fed sodium phosphate with their grain 
ration on alternate days, and concluded that one of the principal 
reasons why cows often fail to maintain a high production record 
in successive years is because their rations are deficient in mineral 
matter. 
The work of Welch (24), of Hart and Steenbock (15), and of 
Kalkus (19) on the relation of the iodine content of the ration to 
hairlessness and goiter in the newly born young of many classes of 
farm animals is another phase of the problem. The results of these 
three separate investigations have, given quite conclusive proof that 
the prevalence of goiter and hairlessness in young animals in certain 
regions is due to improper functioning of the thyroid gland, caused 
by lack of iodine in the rations of the pregnant mothers, which can 
in turn be traced to lack of iodine in the soil and drinking water of 
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