0141647 



a moderate decline within a few hours. Allcroft (1951) found 

 blood lead levels in calves up to 4 ppm within 12 hours of 

 ingestion, a value which fell to 1 to 1.5 ppm in the following 48 

 to 72 hours, but remained elevated above background levels for one 

 to two months. Zmudski et al . (1983) found that maximum blood 

 lead levels in calves occurred six hours after intake of the 

 metal. After 12 hours only about one half of the peak concentra- 

 tion remained, but this level was still in excess of 10 times 

 background. Sheep blood lead levels were shown to peak 4 hours 

 following ingestion of lead acetate (Blaxter, 1950b). Buck et al . 

 (1976) suggested that bovine blood levels from 0.10 to 0.35 ppm 

 were significant as a primary etiological agent or as a predis- 

 posing or contributory factor in lead toxicity. Background blood 

 lead levels up to 0.21 ppm in cattle have been reported by Ruhr 

 (1984). Similar background levels for horses range from 0.04 to 

 0.26 ppm. These values compare favorably with those reported for 

 cattle (0.02 to 0.20 ppm), horses (0.04 to 0.25 ppm) and sheep 

 (0.02 to 0.25 ppm) by Puis (1981). 



Burrows et al . (1981) found blood lead concentrations of 0.35 

 ppm or greater in nine percent of 118 horses and ponies he sampled 

 in the North Idaho silver/lead belt. Two of these horses had 

 blood lead levels of 0.7 ppm, but none of the horses exhibited 

 signs of clinical toxicosis. It has been shown that high to toxic 

 levels of zinc intake will prevent clinical signs of lead toxico- 

 sis in horses. This may help explain observed cases of high blood 

 lead levels where no signs of clinical toxicosis were observed 

 (Willoughby et al . 1972b). Several horses investigated by Schmitt 

 et al. (1971) displayed symptoms of advanced lead toxicosis at 

 blood lead levels ranging from 0.20 to 0.34 ppm. It is evident 

 from the literature that a great deal of variation exists in indi- 

 vidual animal absorption, excretion or metabolism of lead 

 (Dollahite et al. 1978, Zmudski et al. 1983). Attempts to use 

 more specific blood parameters such as delta-aminolevul inic 

 dehydratase (ALA-D) and blood-free erythrocyte porphyrins (FEP) to 

 determine the level of blood lead have met with limited success. 

 Osweiler and Ruhr (1978) found a good correlation (r = 0.9) of FEP 



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