| Methane produced during anaerobic fermentation in the rumen is an energy loss to the host animal and contributes to emissions of greenhouse gases into the environment. Reducing methane emission has implications for efficient animal production but also for global environmental protection. This research was conducted to investigate the effects of vegetable oils and unsaturated octadeca carbon fatty acids on ruminal fermentation, methanogenesis and mechanism involved.Experiment 1. Three types of vegetable oils rich in different content of unsaturated octadeca carbon fatty acids were investigated on in vitro methanogenesis at different inclusion levels. Rapeseed, soybean and linseed oil were added to basal subatrate at levels of 0,3,5 and 7% of substrate DM, respectively. Rapeseed oil had minor effect on methane emission, Soybean oil at 7% inclusion level and linseed oil at all levels decreased methane emission significantly (P<0.05); Methane formation was decreased linearly by increasing level of oils. Three types of oils changed fermentation pattern significantly, Molar proportion of acetate and butyrate decreased and propionate proportion increased significantly with increasing unsaturation of fatty acids in vegetable oils; Elevating vegetable oil level significantly decreased molar proportion of acetate and butyrate and increased propionate proportion. From the present study, it is postulated that the effect of vegetable oils on methane emission is concerned with the type and inclusion levels.Experiment 2. This study was carried out to investigate effects of type and level of octadeca carbon fatty acids (C18-fatty acids) on rumen fermentation, methane emission and populations of ruminal microbes using an in vitro gas production technique. Four types of C18-fatty acids, stearic, oleic, linoleic and linolenic acids, were added at levels of 0,35 and 70 g/kg of substrate dry matter (DM), respectively. Total deoxyribonucleic acid (DNA) was extracted from ruminal microbes, and populations of rumen microbes were determined by a real-time quantitative polymerase chain reaction. The 24 h gas production (GP) and methane emission were decreased by type, level and their interaction (P<0.001). Compared to the control, C18-fatty acids had little effect on pH, ammonia N and total volatile fatty acids (VFA). However, the fermentation patterns were changed, reflected by lower proportion of acetate and higher propionate with increasing levels and unsaturation of C18-fatty acids (P<0.001). Methanogens and protozoa populations relative to total bacterial 16S rDNA were decreased by linoleic and linolenic acids, with the linolenic acid addition being most efficient. However, addition of these unsaturated C18-fatty acids also inhibited growth of fibrolytic microbes including fungi, Fibrobacter succinogenes and Ruminococcus flavefaciens. From the present study, it is inferred that there is an effect of unsaturated C18-fatty acids in suppressing methanogenesis, probably mediated by direct action against the rumen microbes involved in methane formation.Experiment 3. This study was carried out to investigate the effects of mixtures of linoleic and linolenic acids on ruminal fermentation and methane emission using an in vitro gas production technique. Mixtures of fatty acids were added to basal substrate at a level of 50 g/kg DM, with linoleic to linolenic acid ratios at 0:0; 100:0; 80:20; 60:40; 50:50; 40:60; 20:80 and 0:100. A non-supplemented substrate was employed as control. The 24 h gas production and methane formation were significantly depressed by any mixture of fatty acids (P<0.05), the effect being pronounced with increasing ratio of linolenic acid. Mixtures of fatty acids except linoleic acid alone increased pH of fluid. All treatments had no significant effect on ammonia nitrogen and microbial mass. Total VFA increased with the increasing ratio of linolenic acid, with significantly higher in linolenic than in linoleic acid alone. The fermentation patterns were also changed, reflected by lower proportion of acetate and higher propionate with the increasing ratio of linolenic acid (P<0.05). It is inferred that reduction in methane emission is associated with the degree of unsaturation of C18 fatty acids.Experiment 4. Effects of linolenic acid (LNA) at different substrate type on ruminal fermentation, methanogenesis and microbes were investigated in vitro. The experimental design was a 2×5 factorial arrangement. Linolenic acid was added at levels of 0 and 50 g/kg of substrate DM, with corn meal to Chinese wild rye meal ratios at 100:0,70:30,50:50,30:70 and 0:100. The 24 h gas production and methane formation were depressed significantly by adding LNA (P<0.001). LNA addition and increasing ratio of wild rye meal in substrate enhanced fluid pH significantly (P<0.05). Addition of LNA decreased total VFA, acetate and butyrate molar proportion and increased propionate proportion significantly at all substrate type (P<0.001). The fermentation patterns were significantly changed (P<0.001), with lower proportion of acetate and higher propionate, by increasing ratio of corn in substrate. Methanogens and protozoa population were decreased by LNA addition regardless of substrate type (P<0.001). Reducing ratio of corn in substrate enhanced Methanogens and protozoa numbers (P<0.05). There was a significant interaction between LA and substrate type on microbes involved in methane formation (P<0.05). From the present study, it is demonstrated that there is a significant effect of LA addition on suppressing methanogenesis, mediated probably by a direct action against the rumen microbes involved in methane formation.Experiment 5. This study was conducted to investigate the effect of linolenic acid addition on ruminal methane production and fermentation characteristics in the rumen of sheep fed diets containing different ratios of forage to concentrate (F/C). The experimental design was a 4 X 4 Latin square with 2×2 factorial arrangement of treatments. Eight male Hu sheep were paired with fistulated and not fistulated each at the beginning of the experiment. Four pairs of sheep were fed a forage-rich diet without or with LNA, a concentrate-rich diet without or with LNA. Addition of LNA decreased enteric methane emission by 17.3 and 33.8% in forage-and concentrate-rich diet, respectively. A significant interaction was observed among the basal diet, LNA addition and methane production (P<0.05), with the magnitude of response being greater for the low F/C ratio diets. Ruminal pH was increased significantly by inclusion of LNA (P<0.05). Diet type had minor effect on total VFA, while LNA addition decreased total VFA significantly (P<0.05). Addition of LNA decreased molar proportion of acetate and butyrate, and increased molar proportion of propionate in concentrate-rich diet (P<0.05), but had little effect on the fermentation pattern in forage-rich diet (P>0.05). Ammonia-N concentration and microbial protein mass were decreased significantly by inclusion of LNA (P<0.05). Methanogen and protozoa population were decreased significantly by addition of LNA, while not affected by F/C or their interaction. Reducing F/C significantly inhibited the growth of fungi. However, LNA addition and their interaction had minor effect on fungi population. For fibrobacterial microbes, addition of LNA promoted the growth of R. flavefaciens and R. albus significantly, while had little effect on F.succnogen. Reducing F/C decreased R. albus population significantly, while had minor effect on R. flavefaciens and F.succnogen. There were no interactions between F/C and LNA addition on all the microbes. It is suggested that interactions of fat with the basal diet in the rumen have to be taken into consideration to develop effective feeding strategies against ruminal methane formation.In summary, the unsaturated octadeca carbon fatty acids and vegetable oils decreased methane emission and changed fermentation pattern significantly. Inclusion of unsaturated fatty acids is one of the effective methods to reduce energy loss to the host animal and provide theoretical basis for a decrease of greenhouse gases into the environment.
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