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

Abstract

ABSTRACT The current literature lacks information on ruminal microbial metabolism in response to high selenium (Se) concentration in the diet. The current study was performed to investigate changes in ruminal fermentation when high concentration of Se was administered in mixed ruminal cultures in fermentors. Two mature beef cows, fitted 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 mg/kg of Se addition. Orchardgrass hay (20 g of DM/d) containing 0.12 mg/kg of 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 mg/kg over the 11-d adaptation period. Culture pH averaged 6.04 and was not affected by treatment. Total VFA concentration averaged 52.2 and 55.5 mM in the control and Se treatment cultures, respectively, and addition of Se did not affect the total VFA concentration. Molar proportions of acetate and propionate did not differ because of Se addition, resulting in a similar acetate-to-propionate ratio. However, addition of Se tended to increase (P = 0.09) ammonia-N concentration and methane production (P = 0.10). Selenate-respiring microorganisms were detected by the most probable number enumeration technique in 3 of the 4 replications receiving Se. Addition of 50 mg/kg of Se in orchardgrass-hay diet had no negative effects 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 mg/kg would not interfere with in vitro ruminal metabolism by microbiota and that some adaptation of Se-reducing microbes may occur.