EFFECT OF TRACE-ELEMENTS ON POPULATION-DYNAMICS - SELENIUM DEFICIENCY IN FREE-RANGING BLACK-TAILED DEER

The effect of the trace element selenium on black-tailed deer (Odocoileus hemionus columbianus) was studied in northern California. The role of selenium was evaluated by supplementing free-ranging adult females with selenium, measuring fawn production before weaning, and comparing to unsupplemented controls. Whole blood selenium levels (mode = 24 mug/kg) of unsupplemented animals were low, and 95% of free-ranging deer had inadequate levels according to livestock standards. There were no differences in whole blood selenium levels among sexes, ages, or seasons. However, there were significant differences between spring blood samples over the years. Selenium supplements increased preweaning fawn survival from 0.32 fawns/female to 0.83 fawns/female. The assumption that free-ranging wild ruminants are not normally susceptible to trace mineral deficiencies because adaptations to deficiencies occur over geological time was not supported.