Aldrin intoxication and clearance of associated dieldrin residues in a group of feedlot cattle.

A sudden onset of bizarre neurologic dysfunction was found in 8 of 90 mixed-breed feeder calves. Seven other calves were dead, and 3 more died during the next week. A diagnosis of organochlorine toxicosis was made when rumen and abomasal contents from 1 of the calves revealed 22.4 and 20.6 micrograms of aldrin/g of ingesta, respectively. Complete feeds retrieved from self-feeders contained 54 and 528 micrograms of aldrin/g of feed. The initial concentration range in fat from 40 live calves was 6.01 to 42.44 micrograms of dieldrin/g of fat. Additional fat samples were analyzed to verify residue compliance until the entire herd was clear of residue 18 months after removal of the contaminated ration. The range of apparent half-lives for dieldrin in body fat of heifers and steers was 69 to 231 and 53 to 116 days, respectively. These findings demonstrate the considerable variability in apparent half-life of dieldrin in field cases. In cases of dieldrin-contaminated livestock, veterinarians and regulatory personnel must accurately determine the necessary slaughter withholding times so that informed economic decisions are made in the best interest of the producer while enhancing the probability of a safe food supply. Excretion rates of dieldrin from field-contaminated cattle may not be consistent with results obtained under experimental conditions.