MINERAL METABOLISM 371 



syinploms. It has been suggested that ihe liornione may luiulioii by 

 (oiitrolling ihe permeability ol kichiey membranes to Ca++ and thus 

 limiting the rate of excretion. 



Whenever the diet is low in calcium, excretory losses from the blood 

 are replaced with Ca++ drawn from the skeleton. Teeth probably do 

 not serve as a useful reservoir in such cases. Conversely, when calcium 

 is absorbed in Jaige (juantities, the excess is stored in the skeleton. 

 Prolonged excess assimilation of calcium can lead to the abnoiinal 

 deposition of insoluble salts, particularly as kidney stones. 



7he quantity of calcium needed by animals depends upon the 

 species, rate of growth, physiological activity, and diet. The last is 

 especially important for this ion, since calcium forms so many in- 

 soluble salts rendering it unavailable for intestinal assimilation. Thus 

 phytic acid (page 351) can be sufficiently plentiful in plants to precipi- 

 tate the calcitun and reduce its absorption below the level needed. 

 Abnormally large concentrations of phosphate have a similar effect, as 

 does a deficiency of vitamin D. 



Daily allowances with a safety margin have been set at 1.0 g. of 

 Ca++ per day for adults. Pregnant and lactating women should re- 

 ceive, respectively, 1.5 and 2.0 g. per day. Children should receive from 

 1.0 to 1.4 g. daily, depending on age. Milk, legumes, eggs, and vege- 

 tables are the best sources. 



Daily allowances for dairy cattle have been recommended as follows: 

 8 g. for animals weighing 100 lb., 14 g. at 400 lb., 15 g. at 600 to 800 

 lb., 12 g. at maturity (1,200 lb.), 22 g. during the latter part of preg- 

 nancy, and 1 g. per lb. of milk produced during lactation. It is sug- 

 gested that daily rations for beef cattle should contain 20 g. of Ca + + 

 at 400 lb. live weight and 15 g. at 1,000 lb. Bulls should receive 24 g. 

 at 600 lb. and 18 g. at 1,800 lb. Wintering calves and yearlings are 

 allotted 16 g. and animals in the feed lot 20 g. 



Young pigs of 50 lb. should receive 7.4 g. of calcium daily. At 100 

 lb. the recommendation is 13.7 g., and at 200 lb. it is 17.9 g., which is 

 suitable for larger hogs. Pregnant animals and young boars should be 

 fed 16.4 g. daily, and lactating sows and breeding boars from 27 to 41 

 g. of calcium. 



Starting chick rations should contain 1 per cent calcium, increased 

 to 2.25 per cent for laying and breeding hens. The last groups may 

 receive the element in the form of oyster shell fed "free choice." Tenta- 

 tive allowances for turkeys are 2 per cent of the ration for poidts and 

 2.25 per cent for breeding birds. 



Protein concentrates of animal origin, such as tankage and fish 



