0141686 



The zinc content of milk may indicate relative dietary zinc 

 exposure. Miller et al. (1965a) found a good correlation of blood 

 serum zinc and zinc levels in milk up to 1000 ppm dietary zinc. 

 Diet levels above 1000 ppm did not produce any significant 

 increase in milk zinc concentrations. The mammary glands appar- 

 ently selectively exclude zinc at higher levels. Puis (1981) has 

 reported criteria on zinc levels in milk for cattle, horses and 

 pigs. Few studies have been completed on the effects of varying 

 amount of heavy metals in diets on metal concentrations in milk 

 for horses, swine or sheep. 



In summary, both milk and hair may give a gross, regional 

 indication of zinc exposure. More specific information may be 

 obtained through analyses of pancreas, kidney, liver and blood 

 serum, the latter being the most available and probably the 

 easiest to obtain. Existing experimental data should be suffi- 

 cient to interpret the significance of observed zinc levels in 

 serum. 



2.4.2 Livestock zinc hazard levels 



Studies reporting zinc concentrations in livestock fluids, 

 tissue and hair are listed in Tables 22, 23, 24 and 25. This data 

 base was used to determine zinc hazard levels in the following 

 sections . 



2.4.2.1 Toxic zinc hazard levels for cattle 



Background cattle serum zinc levels range from the 0.7 to 1.4 

 ppm reported as normal by Puis (1981) up to the 1.9 ppm reported 

 by Ott et al. (1966d). There is apparently a range (5.2 to 7.6 

 ppm) which may be both toxic and nontoxic or in which toxicosis 

 may be subclinical such as the slight reduction in milk production 

 observed by Miller et al . (1965a). The toxic level of zinc in the 

 blood serum of cattle was reported as 5.2 to 7.5 ppm (Puis 1981) 

 (Table 26) . Data found in the reviewed literature generally 

 support this range. All values <7.6 ppm zinc in cattle blood 

 serum were reported to be nontoxic (Table 24). All values in 

 excess of 7.6 ppm were associated with toxicity. Background 



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