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Effect of nitrate and hydrogen addition on methane production in vitro.

M. E. Rendon



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Effect of nitrate and hydrogen addition on methane production in vitro.
M. E. Rendon*, S. L. Ratiff, J. McDermott, J. Scott, R. Rha, R. Kohn. University of Maryland College Park, MD.

It is theorized that nitrate (NO3) decreases production of enteric methane (CH4) by using hydrogen (H2), a substrate for methanogenesis. We hypothesized that adding gaseous hydrogen (H2(g)) with NO3- would reverse NO3 inhibition of CH4 in vitro. The effect of NO3 and H2(g) on CH4 and volatile fatty acid (VFA) production was analyzed in 2 runs of in vitro fermentation of corn grain and timothy hay. The treatments with corn were control (C), C + NO3 (CN) and C + NO3 + H2(g) (CNH); and for timothy hay were control (T), T + NO3 (TN) and T + NO3 + H2(g) (TNH). Nitrate was included in the flask at 3% of DM. The 2 runs differed in where the H2(g) (60 mL) was placed. In run one, the H2(g) was placed in a balloon attached to the top of flask; and in run 2, H2(g) was incorporated directly into the headspace of the flask. The effect of additive on total CH4 production and VFA concentration were evaluated with a mixed model using JMP Pro 14.1 (SAS Institute Inc.). In run one, CH4 production (mL) in C was 4.94 but was lower (P < 0.03) in CN (2.81) and CNH (1.61). In the same way, CH4 production (mL) in T was 4.04 but was lower (P < 0.0001) in CN (0.71) and CNH (0.76). In run 2, both NO3 and H2(g) negatively affected (P < 0.006) the production of CH4 for C, CN and CNH (5.67, 2.81, 1.48 mL). The CH4 production differed (P < 0.0005) in timothy hay treatments with highest in T (2.96) and lowest in TN (0.49) and TNH between the 2 (1.54). In the first run, for both corn and timothy hay, VFA production (% of total VFA) was not affected (P > 0.05). In the second run, production of acetic (3.88, 3.37, and 2.59%) and propionic (1.59, 1.35, and 1.03%) acids in C, CN, and CNH, respectively, decreased (P < 0.001) with inclusion of NO3 and decreased more with H2(g). With timothy hay, acetic acid production decreased (P < 0.02) only for TN compared with T and TNH (2.92, 2.36, 3.08% for T, TN, TNH, respectively). Effects of NO3 and H2(g) on VFA production were inconsistent. Addition of NO3 decreased methane production in vitro, and the effect was sometimes reversed by adding H2(g).

Keywords: nitrate, hydrogen, methane production.

Biography: My name is Elizabeth Rendon, I have a master's degree in animal sciences from the University of Antioquia, Colombia. I am currently in my last year of Ph.D. in Animal Sciences from the same university. I am doing my internship in Dr. Kohn's laboratory at the University of Maryland, College Park. We are working on the evaluation of the inclusion of nitrates in the diet to reduce methane production at the in vitro level because our interest is to contribute through animal nutrition to the reduction of greenhouse gases that are increasing global warming