Effect Of Malic Acid And Octadecanic Fatty Acids On Rumen Fatty Acids Metabolization And Methane Production In Vitro

The objective of this study was to evaluate the effect of malic acid on biohydrogenation of unsaturated fatty acids and to confirm to the relationship of unsaturated degree of fatty acids and methane inhibition in rumen. This study included two portions:The first portion of the present study was to evaluate the effect of malic acid supplementation in rich-DHA diet on biohydrogenation of unsaturated fatty acid using rumen-simulation technique (RUSITEC). This experiment was designed randomly. Treatments were as follows: base diet rich in DHA (CON); CON diet with 10 mM malic acid (Trt1); CON diet with 20mM malic acid. This experiment was repeated in two-week intervals. Experiment period was duration 7 d including 6 d for adaption and 1d for sampling. The profiles and concentration of fatty acids and the pH, the acetate concentration in fermentation fluid was similar between CON, Trt1 and Trt2. However, the concentration of propionate, butyrate and TVFA in fermentation fluid increased notably in Trt1 and Trt2 compared with CON. The ratio of acetate and propionate decreased markedly in Trt1 and Trt2 compared with CON.The second portion of the present study was to determine the effect of different unsaturation degrees of fatty acids (stearic acid-SA; oleic acid-OA; linoleic acid-LA; linolenic acid-LNA) and different concentrations of malic acid (0, 5, 10 mM) on methane release, rumen fermentation, protozoa count and total gas production using automated cumulative gas production estimation system in vitro. The experiment duration was 36h, each treatment contained three bottles. This experiment was repeated in two-week intervals. Supplementation with fatty acids decreased the methane release significantly in every treatment except for SA compared with CON. Moreover, the most effective inhibition was observed in LA. Compared with CON, pH of fermentation fluid increased, protozoa count and total gas production decreased in treatments when addition of fatty acids. Supplementation malic acid in diets, the concentration of propionate increased in fermentation fluid, the pH of fermentation fluid and methane release decreased. Based on the addition of malic acid (MA5 and MA10), the methane release, total gas production and protozoa count all decreased significantly with the unsaturated degree of fatty acid increasing. However, the difference between LA and LNA was not significant.Results from the current study indicated that malic acid had no effect on TVA accumulation and stearic acid decrease in culture fluid. Thus, we concluded that addition of malic acid in rich-DHA diet had not changed the biohydrogenation of unsaturated fatty acid in rumen. Addition of fatty acids in diet could inhibit the methane release significantly. However, our results confirmed that unsaturated fatty acid-mediated depression in methane production was not directly associated with the degree of unsaturation degree of the fatty acids.