APPETITE OP SWINE 
385 
found that calcium added to a corn ration fed to young pregnant 
swine affected the dams as well as the farrowed pigs favorably, 
making them larger and stronger. 
Recent results of Evvard and Dox^® indicate that young swine 
choose most optimum amounts of calcium carbonate when same 
is allowed at free-choice, this being compared to theoretical al- 
lowances mixed with the feed. The Free-Choice-F'ed pigs having 
the carbonate continuously before them made better growth like- 
wise, than where none was allowed; the basal grain ration of 
Indian corn (maize) and Linseed Oil meal (flax grain minus 
most of the oil) and Wheat Middlings being constant in all re- 
spects. 
Hart and McCollum^^ in some observations with swine find 
that: ‘‘When swine are restricted to corn meal and gluten feed 
little or no growth can be secured, but with an addition of salts, 
making the entire ash content of the ration very similar in 
quality to that of milk, growth approximating that of a normal 
curve was secured to at least 275 pounds. These results are not 
in harmony with the theory that the failure of swine to grow on 
corn alone is due entirely to the incomplete nature of its protein 
content. ’ ’ 
These salts consisted of a mixture of secondary potassium acid 
phosphate and calcium lactate. The effect of these mineral addi- 
tions was pronounced. It is quite suggestive to quote further 
from this paper concerning the ability of swine to select from 
their normal environment some of the materials which they are 
not given when fed by man: “Restriction to mixed grains and 
distilled water did not allow normal growth with swine. This 
emphasizes again the very great importance of either the min- 
eral side of a ration, or as yet unknown factors operative in the 
normal environment of this species, namely, soil roofing, natural 
water, etc.” 
These investigators clearly recognize that the pig, when al- 
lowed access to the great out-of-doors, evidently secures some- 
thing that is quite indispensable for his normal physiologic well- 
being. Just what these substances are, of course, are largely for 
the present unknown, but it is sufficient to say that the appetite 
of the pig guides him rightly in finding that which enables him 
^^Unpublished data from Animal Husbandry and Chemical Sections, Iowa 
Experiment Station. 
27Hart, E. B., and McCollum, E, V. : Influence on Growth of Rations Re- 
stricted to the Corn or Wheat Grain, Jour. Biol. Chem., 1914, XIX, 373. 
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