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an essential element, and all body tissues contain some zinc. 

 Metabolic problems with zinc generally involve a zinc deficiency. 



Although inhalation of industrial dust has resulted in 

 deposition of up to 13,311 ppm zinc in bovine lungs (Dogra et al , 

 1984) the normal route of zinc absorption is through the gastroin- 

 testinal tract. The approximate minimum requirement of zinc in 

 the diet is 40 to 100 ppm for young domestic animals (NRC 1980) . 

 Absorption of zinc is controlled by homeostatic mechanisms when 

 zinc ingestion is within normal ranges. These mechanisms have 

 been shown to become markedly less effective at higher (600 ppm) 

 levels of zinc intake in calves (Miller et al . 1970, 1971). Zinc 

 absorption in humans has been reported to range from 16 to 77 

 percent of the total amount ingested (EPA 1977). Sheep absorbed 

 13 percent of a 39 mg per day zinc diet (Doyle et al. 1974). Zinc 

 deficiency and underweight conditions increase absorption while 

 excessive dietary calcium with phytate decreases zinc absorption. 

 Zinc is primarily excreted in the feces, with lesser amounts in 

 urine. Small amounts are also found in milk, saliva, sweat and 

 hair, the latter is commonly used as an indicator of body zinc 

 levels (Miller et al. 1965b). 



Manifestations of excess dietary zinc include reduced weight 

 gains, anemia, reduced bone ash, decreased iron, copper and 

 manganese in tissues, and diminished utilization of calcium and 

 phosphorus (Ott et al. 1966 c,d). Lameness has been observed in 

 horses receiving up to 186 mg/kg body weight zinc, and severe bone 

 and cartilage abnormalities have been observed in swine receiving 

 268 ppm dietary zinc. Diets with 2,000 to 4,000 ppm zinc have 

 produced an arthritis-like syndrome, internal hemorrhaging and 33 

 to 50 percent mortality in swine (Brink 1959). 



Absorbed zinc binds to sulfyhdryl, amino, imidazole and 

 phosphate groups. Zinc is necessary for several zinc metal- 

 loenzyme and metalloprotein systems, including carbonic anhydrase, 

 carboxypeptidases A and B, alcohol dehydrogenase, glutamic 

 dehydrogenase, D-glyceraldehyde-3-phosphate dehydrogenase, lactic 

 dehydrogenase, malic dehydrogenase, alkaline phosphatase, aldo- 

 lase, superoxide dismutase, r ibonnuclease and DNA polymerase 



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