S. L. Jeffrey,
D. C. Borger,
L. B. Willett 1
The Ohio State University Department of Animal Sciences
According to a survey by the Environmental Protection Agency, 150,000 bovine animals are exposed to toxic concentrations of lead yearly. Of these, 20,000 die. An effective and practical treatment for mediating the effects and body burdens of lead in food-producing animals is needed. The preferred drug for treatment of lead-exposed cattle has been calcium disodium ethylenediamine tetraacetate (EDTA). Toxic effects, related to nonspecific chelation, and relative ineffectiveness suggested an alternative agent be sought. Oral meso-2,3-dimercaptosuccinic acid (DMSA) is the preferred drug for humans, but would probably not survive rumen fermentation. Intravenous DMSA administrations have been effective chelators in experimental animals, so they may work in cattle. Preliminary experiments with intravenous administrations of DMSA in cattle produced decreased blood calcium concentrations (hypocalcemia) and renal failure. The role of calcium on the tolerance and effectiveness of DMSA in cows chronically exposed to lead was evaluated. Four lactating Jersey cows were dosed daily with 1.0 grams of lead for 30 days. As intended, this dosage of lead was not toxic to the cows. On experimental days 14 and 28, cows were allotted one intravenous dose of 0, 10, 20, or 40 mg/kg body weight DMSA and 0 or 11 grams of calcium. No signs of renal failure or hypocalcemia were observed. No lead was detected in the urine of the cows outside the chelation trials. However, DMSA promoted the excretion of urine lead for 20 hours following the DMSA administration. Transient 30 to 50% declines in blood lead concentrations were also observed with the administration of DMSA. Calcium did not affect the activity of DMSA on lead chelation. DMSA is beneficial for chelating lead, but sustained administration of DMSA may be needed to remove sufficient quantities of lead.
1For more information, contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 128 Gerlaugh Hall, 1680 Madison Ave., Wooster, OH 44691; 330-263-3792; e-mail: willett.2@osu.edu