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level of 0.10 to 0.25 ppm lead reported by Puis (1981) for cattle 

 milk. 



2.3.2.2 Toxic lead hazard level for horses 



The basis of the toxic hazard level for lead in horse blood 

 (>0.34 ppm) is, in part, the report of Schmitt et al . (1971) 

 (Table 20). These authors found toxicosis in horses with blood 

 lead levels that ranged from 0.20 to 0.75 ppm. Some of the 

 observed toxicity symptoms in this study were likely due to zinc 

 contamination. Burrows and Borchard (1982) noted that after 

 feeding contaminated hay containing lead acetate (423 ppm) for 5 

 to 6 weeks, ponies exhibited blood levels consistently _> . 3 ppm. 

 These authors found that blood lead concentrations "did not 

 increase consistently at onset of clinical toxicologic signs or 

 just before death". Blood lead levels in four ponies fed lead 

 acetate did not decrease below 0.39 ppm after clinical toxicosis 

 was noted and most concentrations were _> . 5 ppm (Burrows and 

 Borchard, 1982). The 0.34 ppm level is the lowest toxic value 

 found in the reviewed literature that is still above maximum 

 background values. Puis (1981) reported a toxic range of 0.33 to 

 0.50 ppm for this parameter. 



The toxic hazard level for lead in horse urine (0.50-5.0 ppm) 

 is the range noted by Puis (1981). Few data were found from the 

 literature to substantiate this range but it was generally 

 supported by the report of Schmitt et al. (1971). 



The selected lead hazard value of 10 ppm for horse kidney 

 tissue is based on the findings of Buck et al. (1976) and Schmitt 

 et al . (1971). Schmitt et al . (1971) observed toxicity in foals 

 with kidney levels ranging from 4.5 to 20 ppm. The apparent 

 toxicity in this study was likely due in part to high levels of 

 zinc. Eamens et al. (1984) reported one case of clinical toxicity 

 with a kidney tissue level of 8 ppm lead. Puis (1981) noted 

 toxicity ranges for horse kidney tissue of 5.0 to 140 ppm and 20 

 to 200 ppm for chronic and acute poisoning, respectively. Buck et 

 al. (1976) suggested 10 ppm in kidney tissue as diagnostic 

 criteria for lead poisoning. 



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