Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2000
Publication Date: 6/1/2000
Citation: LAWLER, T.L., TAYLOR, J.B., GRINGS, E.E., FINLEY, J.W., CATON, J.S. SELENIUM CONCENTRATION AND DISTRIBUTION IN RANGE FORAGES FROM FOUR LOCATIONS IN THE NORTHERN GREAT PLAINS. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2000. v. 53. p. 7-9. Interpretive Summary: Previous research has shown anticarcinogenic properties associated with supranutritional levels (3 to 4 times recommended amounts) of selenium (Se). It has been suggested that the antioxidative properties of Se might be one mechanism for cancer reductions. Results of cancer preventative studies have also been dependant on the chemical form of Se. Beef, on the average, is the single greatest contributor to human dietary Se in North American and the form of Se found in beef was reported to be highly bioavailable. Geographical region and soil Se concentrations have been reported to be useful in predicting Se concentration of beef. There are limited data available concerning the amount and distribution of Se present in forages throughout the grazing season. Our objectives were to assess Se concentration in diets versus available forage and distribution in forage fractions across the grazing season. Four locations representing high to low Se areas were selected based on presumed Se status of range forages from previous studies. A ranch near Pierre, SD was chosen to represent a high Se area, a ranch near Fargo, ND was chosen to represent a low Se area, a North Dakota Research Extension Center near Jamestown, ND was chosen to represent a moderate Se area, and a USDA-ARS station near Miles City, MT was chosen as an unknown area. Sampling dates of May 29 to June 8 corresponds to the early spring growth of the range forages and July 11 to 20 corresponds to high forage production and decreasing growth. Our data suggest that grass leaves and stems have similar selenium concentrations. Seasonal changes in forage selenium were inconsistent across season. In addition, clipping is an adequate method for assessing selenium concentrations of grazed forage.
Technical Abstract: Locations representing high to low selenium areas were selected to assess selenium concentration in diets vs available forage [masticate (MS) vs clipped grass (TG)] and distribution in forage fractions [grass stems (GS) vs grass leaves (GL)] across season. Locations were near Pierre, SD (PSD), Fargo, ND (FND), Jamestown, ND (JND), and Miles City, MT (MMT). Sampling dates were May 29 to June 8 (JUN) and July 11 to 20 (JUL). At each location, four 27.4 m diameter sites of similar plant species composition were selected and ten 0.25 m2 areas within each site were clipped to a 0.64 cm height. Clipped forage was pooled within site, divided into grasses and forbs, and further subdivided into leaf and stem fractions. After clipping, ruminally cannulated cattle were tethered (one per site) and MS taken via ruminal evacuation techniques. Data were analyzed as a split plot design within location. Forage type (MS, TG, GS, and GL) was the main plot and season the subplot. Dietary Se (MS) concentration did not differ from TG (P > 0.19) within location (3.40 vs 4.07 ± 1.08; 0.11 vs 1.20 ± 0.43; 0.78 vs 0.50 ± 0.17; and 0.29 vs 0.28 ± 0.04 ppm for PSD, FND, JND, and MMT, respectively). Likewise, Se distribution of forage fractions (GS vs GL) was not altered (P > 0.19) within location (4.32 vs 4.86 ± 1.32; 0.38 vs 0.07 ± 0.27; 0.42 vs 0.78 ± 0.24; and 0.51 vs 0.57 ± 0.04 ppm for PSD, FND, JND, and MMT, respectively). At JND and MMT, forage samples in JUN had less (P < 0.04) Se compared with JUL (0.37 vs 0.88 ± 0.16 and 0.27 vs 0.55 ± 0.02 ppm, for JND and MMT respectively). In conclusion, Se concentrations are not different between MS and TG across season; however, much variation seems to occur in Se concentration within location (e.g., FND). Furthermore, Se distribution between GS and GL was not different.