Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2012
Publication Date: February 12, 2013
Citation: Eun, J., Davis, T.Z., Vera, J., Miller, D.N., Panter, K.E., Zobell, D. 2013. Addition of high concentration of inorganic selenium in orchardgrass (Dactylis glomerata L.) hay diet does not interfere with microbial fermentation in mixed ruminal microorganisms in continuous cultures. Professional Animal Scientist. 29(1): 39-45. Interpretive Summary: Selenium (Se) has been recognized for several decades as an essential trace mineral required by all animals. Naturally occurring Se concentrations and forms in forages, grains, and Se-accumulating plants vary considerably, depending on the plant species and especially the Se status of the soil from which they were grown. Although much of the world is troubled with Se deficiencies, Se toxicities are more difficult to control. Cattle and sheep may be poisoned when grazing on Se-accumulating forages. Selenate and Se-methylselenocysteine have been determined to be the predominant forms of Se in Se-accumulating plants such as two-grooved milkvetch (Astragalus bisulcatus) and desert prince’s plume (Stanleya pinnata). The purpose of this study was to determine if a high-Se diet had an effect on rumen fermentation as well as to determine if selenate-respirinig microbes increased indication an adaptation of the rumen to a high-Se diet. The feeding of orchardgrass with 50 ppm Se in in vitro cultures had no negative impacts on ruminal fermentation, as was observed in similar culture pH and VFA concentration. However, there were some changes in microbial metabolism evidenced by increased NH3-N concentration and CH4 production due to Se addition. The increase in selenate respiring microbes suggests that a high Se diet may cause an increase in microbes that are capable of reducing Se to a form that is less bioavailable, and therefore excreted in the feces. Additional research is needed including, speciation of the Se forms in ruminal cultures as well as studies with other ruminants, such as ovine, that are able to tolerate higher concentrations of Se in the diet.
Technical Abstract: The current literature lacks information on ruminal microbial metabolism in response to high selenium (Se) concentration in the diet. We investigated changes in ruminal fermentation when high concentration of Se was administered in mixed ruminal cultures in fermentors. Two mature beef cows, 'tted with a rumen cannula, were grazed on tall fescue pasture and used as donor animals for ruminal contents. Filtered ruminal contents were allowed 11 d of adaptation to diets followed by 3 d of data collection. A dual-flow continuous culture system was used in a completely randomized design (n = 4) to test 2 dietary treatments: control (no Se addition) and 50 ppm Se addition. Orchardgrass hay (20 g DM/d) containing 0.12 ppm Se was added to the fermentors in 2 equal portions at 0800 and 1700 h. Selenium (sodium selenate) was added to the Se addition treatment by gradually increasing the concentration from 2 to 50 ppm over the 11-d of adaptation period. Culture pH averaged 6.04 and was not affected by treatment. Total VFA concentration was unaffected by Se addition as VFA concentration was 52.2 and 55.5 mM in the control and Se treatment cultures, respectively. Molar proportions of acetate and propionate did not differ due to Se addition, resulting in a similar acetate-to-propionate ratio. However, addition of Se tended to increase (P = 0.09) ammonia-N concentration and increased methane production (P = 0.01). Selenate-respiring microorganisms were detected by the most probable number enumeration technique in 3 of the 4 replications receiving Se. Addition of 50 ppm Se in grass hay diet had no negative impacts on ruminal fermentation, as was observed in similar culture pH and VFA concentration. However, addition of Se affected microbial metabolism in the mixed cultures by increasing ammonia-N concentration and methane production. Overall data in this study suggest that the addition of Se up to 50 ppm would not interfere with in vitro ruminal metabolism by microbiota and that some adaptation of Se-reducing microbes may occur.