Selenium (Se) has long been known as a toxic element for animals, and yet we lack good biomarkers for assessing high Se status. Little is known about the mechanism(s) of Se toxicity at a molecular level. In contrast, in Se deficiency, levels of selenoproteins decrease dramatically as tissue Se decreases, and this is accompanied by dramatic decreases in transcript levels for a subset of selenoproteins in most species (Sunde et al. 2016). To explore the effect of high Se status and identify potential biomarkers for high Se status, weanling rodents and day-old turkeys were fed truly Se-deficient diets (<0.005 μg Se/g) supplemented with graded levels of inorganic Se (as selenite) up to 5 μg Se/g.