Maternal and fetal tissue selenium loads in nulliparous ewes fed supranutritional and excessive selenium during mid- to late pregnancy1,2

The objective was to describe the effects of dietary Se concentration and source on fetal and maternal Se load when fed to nulliparous ewes during mid- to late pregnancy. Pregnant, nulliparous ewes (n = 32; 45.6 +/- 2.3 kg; 330 +/- 17 d of age) were randomly assigned to treatment diets. Treatments were 3.5 microg of Se.kg of BW(-1) x d(-1) from the basal Se in the diet (C1X); 75 (S20X) and 350 (S100X) microg of Se.kg of BW(-1) x d(-1), with additional Se from supplemental sodium selenate; and 75 microg of Se.kg of BW(-1) x d(-1), with additional Se from naturally occurring Se-enriched wheat grain (W20X). Treatment diets were initiated at d 50 of pregnancy and continued until slaughter at d 134 +/- 4 of pregnancy. Plasma samples were collected from the ewes immediately before treatments commenced and every 14 d for 70 d. At slaughter, plasma was collected from ewes and their fetuses. Ewes were randomly assigned to 1 of 8 consecutive slaughter days. Maternal and fetal LM, kidney, and liver samples were collected and stored. Tissue and plasma samples were analyzed for Se. Compared with other treatments, S100X resulted in the greatest maternal tissue and plasma Se loads (P < 0.001). However, based on the total amount of Se consumed during the treatment period, efficiency of Se loading was greatest for the W20X treatment. Compared with C1X and S20X, Se loading in fetal tissues and plasma was greater (P < 0.01) for S100X and W20X treatments. In S100X-treated ewes, maternal plasma Se increased rapidly from d 50 to 64 but remained unchanged thereafter. Maternal plasma Se increased steadily throughout the experiment in W20X and S20X ewes, but remained unchanged in C1X throughout the study. Sodium selenate fed at 350 microg of Se.kg of BW(-1) x d(-1) and Se-enriched wheat grain at 75 microg of Se.kg of BW(-1) x d(-1) to nulliparous pregnant ewes neither induced signs of selenosis nor negatively influenced ewe or fetal growth and development. Therefore, ewes in this study were capable of consuming greater than twice the current Se maximum tolerable limit as sodium selenate without experiencing selenosis. Selenium from Se-enriched wheat grain treatment seemed to cross the placenta to the fetus at greater efficiency than did Se from sodium selenate and was equivalent in Se-loading potential to sodium selenate-Se that was fed at nearly 5 times the amount of wheat grain Se.