Effect of nisin on ruminal methane production and nitrate/nitrite reduction in vitro

The suppressing effects of different concentrations of nitrate ( 0, 5, 10, 15, and 20 mM) or nisin ( 0, 5, 10, 15, 20, and 30 mu mol/L) on in vitro methane production were examined with mixed rumen microbes using the in vitro continuous incubation system. The effects of different concentrations of nisin ( 10, 20, and 30 mu mol/L) on in vitro nitrate/nitrite reduction were examined for methane suppression without any nitrate toxicity. The culture mixture consisted of 400 mL of strained rumen fluid from 2 non-lactating Holstein cows fed a diet of oaten hay, alfalfa hay cube, and concentrates ( 35 : 35 : 30) at maintenance level, and 400 mL of autoclaved buffer solution. Methane production was decreased with increasing levels of nitrate. As the concentration of nisin increased from 5 to 30 mu mol/L, methane production was decreased by 14 - 40%. A decrease in acetate to propionate ratio and increase in total volatile fatty acids were observed as the concentration of nisin increased. Toxic nitrite accumulation was unaffected by increasing levels of nisin. In conclusion, nisin improved some of the parameters of ruminal fermentation and inhibited methane production, but did not decrease nitrate toxicity when nitrate was used to inhibit methane production.