0141758 



Excretion of lead occurs through urine, feces, milk, and 

 hair. Studies with rats (Castellino et al . 1966) and sheep 

 (Blaxter and Cowie 1946, Pearl et al. 1983, Bennett and Schwartz 

 1971) suggest that fecal excretion, via bile and by secretion of 

 lead and epithelial exfoliation in the gastrointestinal tract, may 

 be greater than or equal to urinary excretion. Fecal excretion of 

 ingested lead has been reported to range from 82 to 99 percent for 

 sheep (Bennett and Schwartz 1971, Pearl et al. 1983, Blaxter 1950, 

 Fick et al 1976) and high lead levels were found in feces of 

 experimental horses (Willoughby et al. 1972). Chronic exposure to 

 low levels of lead have been shown to produce a near steady state 

 in adult humans, sheep (Pearl et al. 1983), and cattle (Allcroft 

 1951) where metabolic excretion of lead approximately equals lead 

 absorpt i on . 



The estimated minimal cumulative fatal dosage of lead in 

 cattle is 6 to 7 mg/kg body weight per day (Buck et al. 1976). 

 Allcroft (1951) fed lead as lead acetate to an experimental steer 

 at a dose of 5 to 6 mg/kg body weight per day for 33 months before 

 any signs of clinical toxicosis occurred. Hammond and Aronson 

 (1964) observed no effects in cattle consuming 3.0 to 3.5 mg 

 lead/kg body weight per day for several months. Cattle fed 6.25 

 mg lead/kg body weight lead per day died within 24 days (Doyle and 

 Younger 1984), and calves on milk diets containing lead levels of 

 2.7 mg/kg body weight per day died within 20 days (Zmudski et al. 

 1983). Horses have been reported to be poisoned at lead levels of 

 1.7 mg/kg body weight per day. Evidence clearly indicates that 

 livestock can be poisoned by moderately low chronic lead levels. 



Clinical signs of lead poisoning include anorexia, excessive 

 salivation, diarrhea, blindness, muscle twitching, hyperirrita- 

 bility, depression, convulsions, grinding teeth, ataxia, circling, 

 bellowing ("roaring in horses") and incoordination. Lack of 

 muscular control of lips and the rectal sphincter has been 

 observed in ponies (Burrows and Borchard 1982). 



Absorbed lead is initially distributed to soft tissues via 

 the blood. Some of the lead is later redeposited in bone where it 

 accumulates and forms the bulk of the body's lead burden. Lead 



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