Dietary treatment with omega fatty acids mediates in vitro rumen fermentation kinetics and reduce methane emission in water buffalo.

Purpose: To investigate the effect of dietary supplementation of two omega fatty acids on in vitro rumen fermentation, microbial populations, total gas and methane (CH4) production． Methods: Both linoleic and linolenic acids were supplemented at 0 (control), 1, 3, 5 and 7 % of dry matter (DM) in a ration with a high roughage to concentrate ratio (70: 30). Total gas and CH4 were measured at 3, 6, 9, 12 and 24 h of fermentation while pH, volatile fatty acids (VFA), and ammonia nitrogen (NH3-N) concentrations were measured at 24 h using buffalo rumen fluid in an in vitro batch culture system. Microbial populations were determined using 16S-rDNA gene primers by RT-PCR. Results: The results revealed that linoleic acid at 3, 5 and 7 % decreased the concentration of NH3-N (p < 0.05) but linolenic acid at 5 and 7 % increased NH3-N (p < 0.05). A linear decrease (p <0.001) in acetate and butyrate, coupled with linear increase (p <0.001) in propionate was observed in response to treatment. Furthermore, supplementation of 3, 5 and 7 % of both fatty acids linearly (p < 0.001) decreased total gas and CH4 production when compared to the control. The addition of linoleic acid linearly (p < 0.001) decreased the number of protozoa without affecting methanogens, while linolenic acid linearly and quadratically (p < 0.001) reduced the population of both protozoa and methanogens (p < 0.05). Conclusion: Linolenic acid is more effective at a 3 % level in reducing methane production (up to 63 %) in high roughage diets. [ABSTRACT FROM AUTHOR]