Selenium accumulation and loss were measured in adult mallards (Anas platyrhynchos) fed selenomethionine during two experiments. In Experiment 1, both sexes were fed a diet containing 10 ppm selenium for 6 weeks, followed by 6 weeks on untreated feed. Selenium accumulation in liver and muscle of females was described by C=A(1−e−bt). Concentrations of selenium were predicted to reach 95% of equilibrium faster in liver (7.8 days) than in muscle (81 days). The loss of selenium from liver and muscle of females was described by the exponential loss rate equation: C=Ae−bt, with half-times of 18.7 and 30.1 days, respectively. Males reached similar levels of selenium in liver and breast muscle as females and declined to similar levels once selenium treatment ended. In Experiment 2, females were fed increasing levels of selenium until some died. Survivors were switched to an untreated diet and selenium was measured in blood, liver, and breast muscle over 64 days. The same equation as in Experiment 1, C=Ae−bt, was used to describe the loss of selenium from blood and muscle. Halftimes were 9.8 and 23.9 days, respectively. For liver, the equation C C=A1e−b1t+A2e−b2t">= A1e−b1t + A2e−b2t was used. Selenium initially decreased in liver by one-half in 3.3 days, with subsequent half-times of 3.9, 6.0, and 45.1 days.
