A retrospective study on the disappearance of blood lead in cattle with accidental lead toxicosis.

Lead poisoning in cattle and other food animals is of public health significance because of the potential for human exposure to lead through ingestion of contaminated meat and milk products derived from lead-poisoned animals. In Michigan, lead poisoning in livestock is a reportable disease, and positive cattle are quarantined until they test negative (<0.05 ppm blood lead). There is surprisingly little information on blood lead kinetics in cattle. The half-life has been variably reported as 9 weeks and 1-2 months. Because these data did not fit those obtained from cases received at the Michigan State University Animal Health Diagnostic Laboratory, a retrospective study was conducted to review all cases of accidental lead poisoning in cattle between 1990 and 1998. This information is needed to estimate when quarantined lead-poisoned cattle can be released. The results showed that the half-life of blood lead was quite variable and ranged from 48 to 2,507 days. The shortest half-lives (48, 56, and 57 days) were found in a lactating herd of 20-month-old heifers. The longest half-life, 2,507 days, was found in a 9-month-old castrated bull, which ingested a discarded automobile battery. Of the 24 animals monitored, only 8/24 (33%) had half-lives between 6 and 14 weeks. In conclusion, the half-life of blood lead is difficult to predict in accidental cases of cattle poisoning.