372 ANIMAL BIOCHEMISTRY 



meal, arc good sources of calcium. Lcgimie hays are also good, but the 

 grasses and seeds are rather low and should be supplemented. More 

 detailed infonnation on both requirements and sources is presented in 

 tabular form in the Appendix. 



Calcium deficiencies are primarily of three types. One type is char- 

 acteristic of rickets, showing poor bone and tooth development and 

 skeletal malformations. These symptoms are discussed somewhat 

 more fully in connection with deficiency of vitamin D. The second 

 type, failure of the blood-clotting mechanism, represents a symptom of 

 severe, acute lack of calcium and probably does not occur except in 

 laboratory studies. The third type is the nervous disorder, tetany, 

 characterized by intermittent convulsive muscular contractions. Diets 

 high in oxalic acid and similar Ca++-removing agents are occa- 

 sionally encountered in nature and produce tetany. 



Many nutritionists feel that the diets of many Americans are mar- 

 ginally deficient in calcium. The increased consumption of milk, espe- 

 cially among children, has been the most effective means of combating 

 this problem. A greater use of leafy vegetables has also been helpful. 



Animal deficiencies have been encountered under agricultural con- 

 ditions in cattle, sheep, hogs, and chickens. Poor skeletal develop- 

 ment, reproductive disturbances, low milk production, and soft-shelled 

 eggs are the most common symptoms. "Grass tetany" disease may be a 

 Ca++ deficiency and is reported in cattle in localities of Holland, New 

 Zealand, England, and Ireland. In the United States highly acid soils 

 in parts of Florida, Louisiana, and scattered pasture lands in Ohio 

 and along the Atlantic and Gulf coasts produce grasses that are too 

 low in available Ca + + without liming to raise the pH. Occasional 

 acute deficiencies can develop, usually in the form of tetany, when 

 either animals or human beings eat large quantities of plants high in 

 oxalic acid. Rhubarb is probably the commonest cause of this condi- 

 tion. 



Abnormally heavy intakes of Ca++ can lead to physiological dis- 

 turbances, primarily in the form of excessive calcification of joints and 

 deposition of solids in soft tissues. The salts formed are the oxalate, 

 phosphate, and carbonate. Kidney stones are perhaps the most fre- 

 quent manifestation. 



Calcium is excreted in feces as insoluble forms not absorbed from 

 the diet. Moreover, animals on calcium-free rations excrete calcium 

 which presumably must be transferred back through the intestinal 

 wall. Soluble calcium is also lost steadily in the urine, the quantity 

 depending on the state of the animal and the amount absorbed from 

 the diet. 



