386 ANIMAL BIOCHEMISTRY 



occurring in rickets. Reproduction is reduced or blocked with the 

 effects ranging from production of poorly coordinated and partially 

 paralyzed young to complete sterility of both males and females. 

 Enzyme activity is reduced at least for liver arginase. Low manganese 

 contents of certain soils in Holland are now held responsible for a 

 disease characterized in dairy cattle by these same symptoms. Except in 

 poultry other field deficiencies are unknown. 



Poultry show the same experimental abnormalities and are much 

 more prone to the deficiency disease. 1 he condition is likely to be- 

 come widespread when closely enclosed birds are fed rations mainly 

 comprised of corn. In addition to the other symptoms, egg shells are 

 thin and friable, eggs hatch poorly and embryos develop abnormally, 

 and the Achilles tendon of the leg slips from its groove with crippling 

 effect (perosis). 



Manganese is not certainly known to be toxic since very large quan- 

 tities have been fed. However, there is some indication of interference 

 with the metabolism of iron. It is unlikely that manganese toxicity is 

 a practical problem. Elimination of both excessive and normal 

 amounts of manganese occurs by way of the feces, the manganese reach- 

 ing the intestinal tract in the bile with which it is secreted. 



Molybdenum 



Although neither field nor experimental deficiencies in animals are 

 known, molybdenum is believed to be essential to animals because this 

 element is a required component of certain enzymes. Therefore, diets 

 sufficiently low in molybdenum should give disease symptoms even 

 though not yet observed. A deficiency is well recognized in plants, 

 and molybdenum is known to participate in the fixation of at- 

 mospheric nitrogen. Perhaps the feeding of deficient plants might 

 cause symptoms in animals. Apparently the latter need only minute 

 amounts for xanthine oxidase and related iron fiavoproteins. 



Obviously neither allowances nor deficiency states can be described. 

 Nevertheless, the effect of this element on animals has been much 

 studied because of its toxicity. Unlike several of the other elements 

 discussed, molybdenum is rapidly and effectively absorbed by the in- 

 testinal tract. Excretion is primarily urinary and occurs rather rapidly, 

 so that poisoning is likely to occur only with regular ingestion of ex- 

 cessive amounts. 



Toxicity of certain English pastures for cattle has been known for 

 a century, and milder cases have been reported from California, 

 Florida, Manitoba, and New Zealand. Less severe symptoms have been 

 found in sheep, while pigs and horses show no ill effects in the areas 



