378 ANIMAL BIOCHEMISTRY 



animals. In order to provide diets with adequate calcium and phos- 

 phate, feeds are supplemented with bone meal or rock phosphate. The 

 moderate concentrations of fluoride in the former are quite safe. How- 

 ever, the rock phosphates of North Africa and North America con- 

 tain 3 to 4 per cent F", enough to provide 10 times the safe intake 

 when included in feeds. The phosphate rocks of the Pacific and Indian 

 oceans contain less fluoride but still enough to be potentially hazard- 

 ous. The Association of American Feed Control Officials recom- 

 mended in 1955 that the fluorine content of any minerals used in feeds 

 be below 0..80 per cent for cattle, 0.35 per cent for sheep, 0.45 per cent 

 for hogs, and 0.60 per cent for poultry. Furthermore, the amounts 

 used should not raise the fluorine content of the total ration above 

 0.009 per cent for cattle, 0.010 per cent for sheep, 0.014 per cent for 

 swine and 0.035 per cent for poultry. 



It may require a year or more for symptoms of fluorine poisoning 

 to develop in livestock. Then the teeth begin to deteriorate in young 

 animals, bony projections appear on the skeleton, joints thicken, 

 movement is slow and painful. Growth is poor and emaciation is 

 common. Mortality of the young is high, not because they are poisoned 

 but because the mother is physiologically impoverished. There is little 

 transfer of fluoride from mother to ofl^spring through the placenta or 

 the milk. Hence the newborn and suckling animals suffer from starva- 

 tion rather than toxicity. If fluoride poisoning does not begin until 

 after the permanent teeth are fully developed, the teeth are not ad- 

 versely affected and this group of symptoms is not observed. 



Fluoride antagonizes certain enzyme activators and iji vitro inter- 

 feres with enzyme action. Enolase, for example, is a phosphoprotein 

 and requires Mg++ for its activity.' Fluoride inactivates the system by 

 leading to magnesium fluorophosphate. Many of the enzymes depend- 

 ing upon calcium, magnesium, manganese, iron, copper, and zinc are 

 potentially suscej^tible to the presence of F". The occurrence and 

 extent of such inhibitions in the animal have been studied but little. 

 According to one suggestion, fluoride interferes with the metabolism 

 of ascorbic acid, and in another study the ion was found to affect the 

 phosphatase of bone. A great deal more work is indicated. 



Iodide 



Although not known to be essential to plants, iodine occurs in them 

 and is rather abundant in a variety of sea plants. Mammals all ap- 

 pear to need this element in small amounts and ingest it primarily as 

 iodide ion, although organic forms will serve. Once absorbed, iodide is 



