Agronomic biofortification is defined as increasing the bioavailable concentrations of essential elements in edible portions of crop plants through the use of fertilizers. The potential for using Se-containing fertilizers to increase crop Se concentrations and, thus, dietary Se intakes has been demonstrated in Finland, New Zealand, and Australia where it has proven to be both effective and safe.

A pilot study conducted at the Oregon State University sheep center from 2005-2006 for the Oregon Department of Agriculture (Pirelli, unpublished data) showed that high levels of Se applied to pasture (9.1 kg of Selcote Ultra® containing 225 g Se per hectare) resulted in Se concentrations (dry matter basis) of approximately 7 ppm in green forage and approximately 3 ppm in hay made from the pasture. This hay was fed to a small group of pregnant ewes for 100 days, at which time lambs were delivered by caesarian section. Blood tests showed Se concentrations of ewes (median 262; range 161 to 330 ng/mL) and lambs (median 282; range 212-311 ng/mL) were all within the normal reference interval (150-500 ng/mL). No toxic effects were observed clinically.

The purpose of this study was to evaluate Se status in sheep across time after short term exposure to high-Se-fertilized forage compared to a mineral supplement containing inorganic sodium selenite.

Materials and Methods

Three pounds of Selcote (Selcote Ultra®; 10 g Se/kg as sodium selenate) was applied to 15 acres of pasture on February 1, 2007.  The selcote was mixed with nitrogen fertilizer in the form of urea.  A rate of 60 pounds per acre of nitrogen was used as the application rate.

Pasture forage samples were obtained using a grid pattern with one sample generated from 25 subsamples. The pasture forage was sampled at three times (on days 1,10, and 40 relative to the grazing period) to obtain samples for Se analysis. Forage samples were submitted to the University of California, Davis, (Davis, CA) for forage Se analysis.

On March 27, thirty ewes were sorted randomly into two groups.  Ear tags and paint brands were used to identify the ewes.  Blood samples were taken from all sheep.  One group of 15 ewes was moved to the selenium fertilized pasture on March 30.  This group had no mineral supplementation.  The second group was also moved to pasture (non-fertilized) with a 200 ppm selenium sheep mineral mix.  The average intake of mineral supplement was 7.1 g per day per ewe. The supplement also contained 95.0 g/kg calcium, 60.0 g/kg phosphorus, 375.0 g/kg salt (NaCl), 27.0 g/kg magnesium, 60 ppm cobalt, 1,700 ppm manganese, 210 ppm iodine, 1,350 ppm iron, 7,700 ppm zinc, 564,400 I.U./kg vitamin A, 70,550 I.U./kg vitamin D, and 123.5 I.U./kg vitamin E.

The two groups of ewes grazed for approximately 40 days on the pastures.  Post-treatment blood tests were taken on May 9.  The two groups of ewes were combined and treated as a single grazing group with no mineral supplementation.

 Sheep were then bled every 3-4 weeks for approximately 9 months to collect whole blood for Se analysis. Blood was collected into EDTA tubes and shipped on ice to a commercial laboratory (Center for Nutrition, Diagnostic Center for Population and Animal Health, Michigan State University, E. Lansing, Michigan.