Selenium elimination in pigs after an outbreak of selenium toxicosis

May 1996, 150 grower pigs in 5 California counties were exposed to selenium -contaminated feed distributed by a single feed company. Feed samples from 20 herds had a mean selenium concentration of 121.7 ppm dry weight (range, 22.1-531 ppm). In San Luis Obispo County, 52 pigs in 24 herds were exposed to the feed, and 8 pigs died with signs of paralysis. Bilateral symmetrical poliomyelomalacia involving the ventral horns of the cervical and lumbar i ntumescence was evident on histologic examination of spinal cord from affec ted pigs. Of 44 surviving exposed pigs, 33 (75%) exhibited signs of selenos is, including anorexia, alopecia, and hoof lesions. Thirty-nine of 44 pigs (88.6%) had elevated (>1 ppm) blood selenium concentrations. Surviving expo sed pigs were changed to a standard commercial ration containing approximat ely 0.5 ppm (dry weight) selenium. Blood selenium concentrations were deter mined weekly for 46 days following removal of the contaminated feed and wer e compared with values of 20 control pigs fed a standard commercial ration. Mean (CSD) blood selenium concentrations of exposed pigs were 3.2 +/- 2.6 ppm at the initial sampling and 0.4 +/- 0.1 ppm after 46 days. Mean blood s elenium concentrations of less than or equal to 0.3 ppm for control pigs at all samplings were significantly lower (P < 0.001) than concentrations for exposed pigs. Muscle and liver samples of 22 of the 44 exposed pigs were c ollected at slaughter approximately 72 days after withdrawal of the seleniu m-contaminated feed. Muscle samples had a mean selenium concentration of 0. 36 ppm (wet weight). Liver samples had a mean selenium concentration of 1.2 6 ppm (wet weight). One liver sample had a selenium value in the toxic rang e for pigs (3.3 ppm wet weight; reference range, 0.4-1.2 ppm). A l-compartm ent pharmacokinetic model of selenium elimination in exposed pigs was gener ated, and the geometric mean blood selenium elimination half-life was estim ated to be 12 days. The 60-day withdrawal time recommended by the Food Anim al Residue Avoidance Database was considered sufficient to allow safe human consumption of tissues from exposed pigs.