Lead and zinc poisoning and the interaction between Pb and Zn poisoning in the foal

Groups of young growing horses were fed toxic amounts of lead only, zinc only and the same amounts of lead and zinc together. Those fed Pb only developed pharyngeal and laryngeal paralysis ("roaring") whereas those fed Zn only and Pb and Zn together developed the same clinical syndrome which included swelling at the epiphyseal region of the long bones, stiffness and lameness. Anemia and decreased weight gains were most pronounced in animals fed Zn for the longest periods. Animals fed Pb only did not become anemic and weight loss did not occur until after there was an interference in swallowing. The clinical signs and tissue Pb values from animals fed toxic amounts of both Pb and Zn continuously, differed markedly from those present in animals fed comparable amounts of Pb only. Th clinical signs were similar to those caused by Zn poisoning. The hepatic and renal tissue Pb values were approximately twice as high and the epiphyseal and cancellous bone sample results were one half as high as the comparable Pb values from animals fed toxic amounts of Pb only. It appeared that toxic amounts of Zn prevented the development of clinical signs of Pb poisoning in the young growing horse.