THE EFFECT OF SUBCLINICAL SELENIUM TOXICOSIS ON PREGNANT BEEF-CATTLE

A field investigation conducted by the South Dakota Animal Disease Res earch and Diagnostic Laboratory suggested that subclinical selenium to xicosis in pregnant cows may have contributed to an outbreak of aborte d/stillborn calves in a high-selenium region of South Dakota. This stu dy was undertaken to evaluate the relationship between abortion and su bclinical selenium toxicosis in the dam and to assess the effects of s ubclinical selenium toxicosis on the bovine immune system. Fifteen pre gnant cows were fed diets containing 0.25 (control), 6.0, and 12.0 ppm selenium beginning at 80-110 days gestation. Although selenium toxico sis has been reported to cause abortion, this study failed to reproduc e abortions. A single cow in the 12-ppm selenium treatment group gave birth to a weak calf, which subsequently died. This calf had myocardia l lesions consistent with those described for selenium toxicosis and h ad hepatic selenium levels of 9.68 ppm (wet weight). Elevated dietary selenium resulted in the depression of several leukocyte function para meters in pregnant cows. A statistically significant depression in for ced antibody response was identified in both selenium-supplemented gro ups. A significantly diminished mitogenic response to concanavalin A a nd pokeweed mitogen was also observed in the 12-ppm selenium group. Al though a similar pattern of depression was also observed with phytohem agglutinin, differences were not significant. These findings indicate that even in the absence of clinical alkali disease, elevated selenium levels may adversely affect both pregnancy outcome and the bovine imm une system.