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The range of background concentrations of zinc in cattle milk 

 is 2.8 to 4.780 ppm (Dorn et al. 1975, Parkash and Jenness 1967). 

 The toxic hazard level of 8.4 ppm zinc in cattle milk is the level 

 reported by Puis (1981) as indicative of toxicosis. This value 

 was derived from Miller et al„ (1965a) who noted a slight reduc- 

 tion in milk production at that level but no other apparent 

 toxicity to the 24 dairy cows used in the study. 



2.4.2.2 Toxic zinc hazard levels for horses 



The hazard level for toxic zinc concentrations in horse blood 

 is based on only one study provided by Eamens et al . (1984) (Table 

 27). This hazard level should be used with care. The suggested 

 hazard level for toxic concentrations of zinc in whole blood of 

 horses (5-15 ppm) is the range reported by Puis (1981). No 

 additional support data were found in the reviewed literature. 



Diagnostic levels for zinc in horse kidney and liver tissues 

 were reported between 295 to 580 ppm and 1300 to 1900 ppm, 

 respectively (Puis 1981). The limited data of Eamens et al . 

 (1984) suggested ranges of 180 to 580 ppm and 1200 to 1900 ppm 

 zinc in horse kidney and liver tissue respectively may be more ap- 

 propriate. 



The hazard level for the toxic concentration of zinc in horse 

 hair (280 ppm) is based on the very limited data of Lewis (1972). 

 The 280 ppm level was the concentration found in a single horse 

 that subsequently died. The hair of other horses in the study 

 ranged from 140 to 430 ppm zinc. Toxicity was not noted in a 

 number of horses with hair zinc levels above 280 ppm. This level 

 should best be considered as an indication of possible excessive 

 exposure to zinc and as with most hair data, sufficient numbers of 

 animals should be sampled to provide a meaningful statistical 

 confidence. 



2.4.2.3 Toxic zinc hazard levels for sheep and goats 



The toxic hazard level reported for zinc in sheep serum is 

 7.1 to 44 ppm (Table 28). This range was derived from data 

 reported by Ott et al. (1966c). These authors reported reduced 



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