382 ANIMAL BIOCHEMISTRY 



group participating in the transfer of hydrogen and/or electrons. 

 Thus the cytochromes, cytochrome oxidase, certain flavoproteins, 

 xanthine oxidase, and others are iron proteins. Most if not all of 

 these are essential. 



Since most of the iron in animals occurs in the hemoglobin packed 

 into the red cells, the state of this system tends to determine the over- 

 all requirements. Studies with radioactive iron indicate that red cells 

 normally have life spans averaging 127 clays. When these cells disin- 

 tegrate, the hemoglobin is also broken down and the iron released. 

 However, though much of the organic material is excreted, nearly all 

 the iron is retained and used again and again. 



When iron is absorbed by the intestine it combines with a protein to 

 form ferritin, a complex of ferric ion and phosphoprotein reaching 22 

 per cent iron. Ferritin accumulates in the spleen, kidneys, and espe- 

 cially the liver. Reduction of the iron to the ferrous stage releases it 

 to the blood, which transports it to the bone marrow where new 

 erythrocytes form. This storage and utilization system is efficient and 

 little iron is excreted. Severe acute or chronic bleeding may reduce 

 the iron reserves seriously, but losses are otherwise quite small. 



Absorption of ingested iron is dependent to some extent upon the 

 diet. Foods high in phosphate or phytic acid convert the iron to in- 

 soluble salts. Aside from this effect, iron allowances depend upon the 

 physiological status. Infants have relatively high requirements of 200 

 mg./year, normally met in part by iron stored during the gestation 

 period. At 2 years of age the need drops to half this value to rise 

 during adolescence to a high of 350 mg. annually for boys and 500 mg. 

 for girls. In males the requirement drops sharply to 80 mg. yearly 

 but holds at about 300 mg./year for women with increased demands 

 during pregnancy when the fetus begins storing iron. Liver, heart, 

 eggs, yeast, sea foods, seeds, leafy vegetables, meat, poultry, and nuts 

 are good to fair sources of iron. Milk, fats, white flour, polished rice, 

 potatoes, and most fruits are poor sources. Ferrous sulfate is com- 

 monly used in supplementing deficient diets and during later stages 

 of gestation. The efficient storage of iron in the body makes it unneces- 

 sary to consume iron regularly. A feast and famine sequence seems 

 to work as well as any other regimen. Average American diets supply 

 15 to 20 mg. daily, an adequate amount even for child bearing. 



Allowances for farm animals are difficult to set, but deficiencies are 

 not common except perhaps in swine and laying poidtry. Suckling 

 pigs tend to be susceptible to iron deficiency, and 15 mg. daily has been 

 recommended. The tentative requirement for chicks is 9 mg./lb. of 

 feed with about 5 times that amount actually present in standard feeds. 



