0141757 



given (Friberg et al . 1974). Only a small amount of literature 

 exists concerning the long-term carcinogenic effects of low level 

 chronic cadmium poisoning in domestic livestock. 



Zinc is antagonistic to cadmium and the effects of cadmium 

 poisoning have been somewhat attenuated by increasing zinc in the 

 diet. The antagonistic nature of zinc has reduced the risk of 

 exposure to cadmium in some areas polluted by smelters. Simi- 

 larly, supplemental calcium, iron, copper, selenium and ascorbic 

 acid in the diet has decreased the effects of cadmium toxicity. 

 Lead appears to be synergistic and increases cadmium toxicity. 



6.1.3 Lead toxicology 



Lead poisoning is the most common form of heavy metal 

 poisoning in livestock and has been the subject of many reports 

 and literature reviews (Amnerman et al . 1977, Aronson 1972, Buck 

 1970). Ingestion and subsequent absorption of lead in the 

 gastrointestinal tract is the primary mode of absorption in 

 domestic animals although Dogra et al. (1984) found bovine lungs 

 with lead concentrations up to 4268 ppm in industrial areas. 

 Sources of lead include contaminated feed, forage, and soils, 

 along with lead-bearing debris (storage batteries, used crankcase 

 oil, paint, leaded gasoline, etc.). Lead compounds are generally 

 insoluble and some soluble forms (lead acetate) develop insoluble 

 compounds (lead sulfate) in the gastrointestinal tract. Ruminants 

 and nonruminants absorb less than three percent and about 10 

 percent of ingested lead, respectively (National Research Council 

 (NRC) 1972). Research has shown that excessive dietary calcium 

 and phosphorus decrease lead absorption in rats and lambs (NRC 

 1980). High zinc intake has a beneficial effect on lead toxicity 

 in horses (Schmitt et al . 1971, Willoughby et al . 1972) and swine 

 (Hsu et al. 1975). Horses may be more prone to lead poisoning 

 than ruminants, but the higher number of incidents reported for 

 horses may be partially the result of ingestion of higher levels 

 of contaminated soils (Buck et al. 1976). Swine, sheep, goats, 

 and chickens are apparently somewhat resistant to lead intoxica- 

 tion (Damron et al . 1969, Staples 1975, NRC 1980). 



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