The impact of inclusion of essential oils (EO) extracted from Juniperus phoenicea, Satureja calamintha and Mentha pulegium at three levels: 0, 1.66, 3.33 and 6.66 μl/ml of incubation medium, on methane production and rumen fermentation traits of vetch-oat hay was studied in in vitro gas production test, using 200 mg of substrate in a 60 ml graduated syringes. Gas production was recorded at 3, 6, 9, 24, 48, 72 and 96 h. Methane was measured at 3, 24 and 96 h, while pH and ammonia N were analyzed just at 24 h of incubation. At 24 h of fermentation, all doses of EO reduced significantly total gas and methane production (P < 0.05). At the highest concentration and after 24 h, methanogenesis was decreased by 60.98, 57.70 and 64.64% for J. phoenicea, M. pulegium and S. calamintha, respectively. This effect was more pronounced at the end of fermentation (96 h) where reduction in methane production was superior to 72%. However, addition of EO increased pH and decreased significantly ammonia concentration, mainly, for high EO concentrations. The results indicate that these EO had a potential to reduce methanogenesis in the rumen, but further in vitro and in vivo trials are required to search optimum dose which reduce methane production without adversely changing dietary fermentation and rumen function.
Key words: Methane, ammonia, essential oils, Satureja calamintha (Calament), Mentha pulegium (fliou, Menthe pouliot), Juniperus phoenicea (Arar, Genévrier), in vitro gas production test
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