Organic and inorganic selenium: I. Oral bioavailability in ewes1

Abstract

Although the essentiality of dietary Se for sheep has been known for decades, the chemical source and Se dosage for optimal health remain unclear. In the United States, the Food and Drug Administration (FDA) regulates Se supplementation, regardless of the source of Se, at 0.3 mg of Se/kg of diet (as fed), which is equivalent to 0.7 mg of Se/d or 4.9 mg of Se/wk per sheep. The objectives of this study were to evaluate the effects of Se source (inorganic vs. organic) and supplementation rate (FDA vs. supranutritional rates of 14.7 and 24.5 mg of Se/wk) on whole-blood (WB) and serum-Se concentrations. Mature ewes (n = 240) were randomly assigned to 8 treatment groups (n = 30 each) based on Se supplementation rate (4.9, 14.7, and 24.5 mg of Se•wk(-1)•sheep(-1)) and source [Na-selenite, Na-selenate (4.9 mg/wk only), and organic Se-yeast] with a no-Se control group (0 mg of Se/wk). Treatment groups were balanced for healthy and footrot-affected ewes. For 1 yr, ewes were individually dosed once weekly with 0, 4.9, 14.7, or 24.5 mg of Se, quantities equivalent to their summed daily supplementation rates. Serum- and WB-Se concentrations were measured every 3 mo in all ewes; additionally, WB-Se concentrations were measured once monthly in one-half of the ewes receiving 0 or 4.9 mg of Se/wk. Ewes receiving no Se showed a 78.8 and 58.8% decrease (P < 0.001) in WB- (250 to 53 ng/mL) and serum- (97 to 40 ng/mL) Se concentrations, respectively, over the duration of the study. Whole-blood Se decreased primarily during pregnancy (-57%; 258 to 111 ng/mL) and again during peak lactation (-44%; 109 to 61 ng/mL; P < 0.001). At 4.9 mg of Se/wk, Se-yeast (364 ng/mL, final Se concentration) was more effective than Na-selenite (269 ng/mL) at increasing WB-Se concentrations (P < 0.001). Supranutritional Se-yeast dosages increased WB-Se concentrations in a dose-dependent manner (563 ng/mL, 14.7 mg of Se/wk; 748 ng/mL, 24.5 mg of Se/wk; P < 0.001), whereas WB-Se concentrations were not different for the Na-selenite groups (350 ng/mL, 14.7 mg of Se/wk; 363 ng/mL, 24.5 mg of Se/wk) or the 4.9 mg of Se/wk Se-yeast group (364 ng/mL). In summary, the dose range whereby Se supplementation increased blood Se concentrations was more limited for inorganic Na-selenite than for organic Se-yeast. The smallest rate (FDA-recommended quantity) of organic Se supplementation was equally effective as supranutritional rates of Na-selenite supplementation in increasing WB-Se concentrations, demonstrating the greater oral bioavailability of organic Se.

Effect of dietary supplementation with selenium-enriched yeast or sodium selenite on ruminal enzyme activities and blood chemistry in sheep

“…This finding is in agreement with the study by Hall et al (2012) who studied the effects of the Se source (inorganic vs. organic) and supplementation rate (the Food and Drug Administration, FDA vs. supranutritional rates) on whole -blood and serum -Se concentrations in mature ewes. Their results showed that the dose range whereby Se supplementation increased blood Se concentrations was more limited for the inorganic Na-selenite than for the organic Se-yeast.…”

Blood biochemical indicators and concentration of thyroid hormones in heavily pregnant and lactating ewes depending on selenium supplementation

“…According to previous studies (Pavlata et al 2011;Hall et al 2012;Antunović et al 2013;Faixova et al 2016) it is more efficient to utilize organic sources of Se compared to inorganic, as also demonstrated in the present study.…”

“…The most commonly used inorganic selenium supplement in animal feeds is sodium selenite, and organic selenized yeast. According to research in ewes (Hall et al 2012), true digestibility of Se from diets containing selenite showed to be about 50% whereas that from Se-yeast was about 66% with regard to different metabolism. Inorganic selenium is exclusively used for the synthesis of seleno-enzymes whereas organic selenium can be incorporated into any protein, serving as a possible Se storage capacity (Vignola et al 2007).…”

Effect of Selenium Yeast Supplementation on Naturally Acquired Parasitic Infection in Ewes

“…Experimental procedures used in this study were approved by the Institutional Animal Care and Use Committee of Oregon State University and have been described in detail previously [35]. Briefly, 120 mature ewes were randomly assigned to four treatment groups (n=30 each) and received a weekly oral drench of no Se (Se depletion), 4.9 mg Se/week (maximum FDA-allowed concentration; control) as Se yeast (Prince Se Yeast 2000, Prince Agri Products Inc., Quincy, IL), or supranutritional concentrations of 14.7 and 24.5 mg Se/week as Se yeast (3× and 5× the maximum FDA-allowed concentration, respectively).…”