Organic and inorganic selenium: I. Oral bioavailability in ewes

Area of Science:

• Animal Nutrition
• Trace Mineral Metabolism
• Sheep Physiology

Background:

• Dietary selenium (Se) is essential for sheep, but optimal chemical sources and dosages for health are not fully understood.
• The U.S. Food and Drug Administration (FDA) currently regulates Se supplementation at 0.3 mg/kg diet, equivalent to 4.9 mg/week per sheep.
• Understanding Se bioavailability from different sources is crucial for effective supplementation strategies in sheep production.

Purpose of the Study:

• To evaluate the impact of selenium source (inorganic vs. organic) on sheep.
• To determine the effects of varying supplementation rates, including FDA-recommended and supranutritional levels, on selenium concentrations.
• To compare the bioavailability of different selenium forms in mature ewes.

Main Methods:

• 240 mature ewes were assigned to 8 treatment groups, receiving 0, 4.9, 14.7, or 24.5 mg of Se/week from Na-selenite, Na-selenate, or organic Se-yeast for one year.
• Whole-blood (WB) and serum-Se concentrations were measured every 3 months.
• WB-Se was also measured monthly in control and 4.9 mg/wk Se groups to monitor dynamic changes.

Main Results:

• Ewes without Se supplementation experienced significant decreases in WB-Se (78.8%) and serum-Se (58.8%) over the study period.
• Organic Se-yeast at 4.9 mg/wk was more effective at increasing WB-Se than Na-selenite at the same rate.
• Supranutritional doses of Se-yeast increased WB-Se in a dose-dependent manner, while Na-selenite showed a limited dose-response range.

Conclusions:

• Organic Se-yeast demonstrates superior bioavailability compared to inorganic Na-selenite in sheep.
• The FDA-recommended Se supplementation rate of organic Se-yeast is effective in raising blood Se levels.
• Supplementation strategies should consider the source of selenium to optimize bioavailability and efficacy in sheep.