0141656 



parameter (Table 21). Puis (1981) reported sheep blood lead 

 levels in the range of 1.0 to 5.0 ppm were toxic. 



Toxic lead concentrations in sheep urine were noted by 

 Blaxter (1950a) and ranged from 0.28 to 0.81 ppm. The 0.28 to 

 0.32 ppm toxic hazard level for lead in sheep urine should be used 

 with caution until more data are available. 



Toxic lead levels in sheep kidney and liver tissues were 

 reported as 5 to 200 ppm and 10 to 100 ppm respectively (Puis 

 1981). With minor exceptions, data in the reviewed literature 

 tended to support these ranges. 



The toxic hazard level for lead concentrations in sheep wool 

 (25 ppm) was reported by Puis (1981). No data were found in this 

 review to substantiate this value. 



2.4 Zinc 



2.4.1 Zinc literature review 



Zinc is an essential element and most animals can tolerate 

 relatively high dietary levels. Few cases of natural zinc 

 poisoning of livestock have been reported in the literature. Most 

 episodes of poisoning involve contamination of livestock feed 

 (Allen 1968, Grimmett et al . 1937, Sampson et al . 1942, Davies et 

 al. 1977). Experimental zinc toxicosis in livestock has been 

 studied and described in several reports and much of these data 

 are reviewed here. 



The uptake of toxic amounts of zinc affects many organs 

 directly or interferes with the metabolism of several other 

 elements, notably iron, copper, calcium and cadmium. Cadmium acts 

 synergisticly with high levels of zinc, enhancing the toxic 

 effects of zinc (Thawley et al . 1977). Cadmium also tends to 

 reduce the absorption and retention of zinc (Miller 1969) . Zinc 

 absorption is higher in young animals than in older animals, 

 making them more susceptible to zinc poisoning (Davies et al. 

 1977). The degree to which the diet composition affects this re- 

 lationship remains unresolved. Diets containing 200-400 ppm zinc 

 have been shown to produce clinical copper deficiency in diets 



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