PSVI-26 - Response of cows to high unsaturated fatty acid diet from the insights of methane production, rumen fermentation and metagenome

Abstract: The purpose of this study was to investigate the effect of unsaturated fatty acids (UFA) content on rumen fermentation, methane (CH₄) emission and mechanism of reducing methane production. Ten multiparous Holstein cows with two parity and similar milk in days (209 ± 10 d) were randomly divided into two groups. The two groups were fed two different UFA percentage (low unsaturated fatty acids: LUFA=35.5 ± 0.21%; high unsaturated fatty acids: HUFA=80.60 ± 0.50%) with similar fat content (59.5 ± 0.1 g fat/ kg DM). Rumen fermentation parameters and gas production were analyzed using t test in SAS version 9.4 software (SAS Institute Inc., Cary, NC, USA). The rumen microorganism and abundance of KEGG pathways were compared using linear discriminant analysis effect size (LEfSe). Our study found that there was no significant difference in the production of primary volatile fatty acids (VFAs) between two treatment groups (P < 0.05), but the ratio of acetate to propionate, ammonia nitrogen (NH₃-N), iso-butyrate and iso-valerate in HUFA group was significantly lower than LUFA group (P > 0.05). Furthermore, compared with LUFA group, methane (CH₄) and carbon dioxide (CO₂) emissions of HUFA group decreased significantly (21.60% and 12.48%, respectively, P < 0.05). Meanwhile, CH₄ yield per kilogram of dry matter intake (DMI) and per kilogram of organic matter intake (OMI) decreased significantly in HUFA group (15.17% and 15.65%, P < 0.05). Metagenome results showed that, for differential bacteria, the abundance of Bacteroidetes and Parabacteroides significantly increased in HUFA group cows (|LDA| > 2 and P < 0.05), while that of Clostridium, Butyrivibrio, Treponema, Coprobacillus, Bacillus and Acholeplasma was higher in LUFA group cows (|LDA| > 2 and P < 0.05). For differential archaea, the Euryarchaeota and Methanobrevibacter was significantly lower in the HUFA group cows (|LDA| > 2 and P < 0.05). Through functional analysis, we found that the increase of dietary UFA content inhibited the pathway of methane metabolism in rumen (|LDA| > 2 and P < 0.05), while promoted the enrichment of carbohydrate and nitrogen metabolism pathway in HUFA group (|LDA| > 2 and P < 0.05). These results indicated that increasing the proportion of UFA could inhibit methane metabolism pathway in rumen by toxic effect on methanogens, so as to reduce rumen methane production.