In vitro rumen fermentation kinetics, metabolite production, methane and substrate degradability of polyphenol rich plant leaves and their component complete feed blocks

BACKGROUND: This experiment aimed at assessing polyphenol-rich plant biomass to use in complete feed making for the feeding of ruminants. METHODS: An in vitro ruminal evaluation of complete blocks (CFB) with (Acacia nilotica, Ziziphus nummularia leaves) and without (Vigna sinensis hay) polyphenol rich plant leaves was conducted by applying Menke’s in vitro gas production (IVGP) technique. A total of six substrates, viz. three forages and three CFBs were subjected to in vitro ruminal fermentation in glass syringes to assess gas and methane production, substrate degradability, and rumen fermentation metabolites. RESULTS: Total polyphenol content (g/Kg) was 163 in A. nilotica compared to 52.5 in Z. nummularia with a contrasting difference in tannin fractions, higher hydrolysable tannins (HT) in the former (140.1 vs 2.8) and higher condensed (CT) tannins in the later (28.3 vs 7.9). The potential gas production was lower with a higher lag phase (L) in CT containing Z. nummularia and the component feed block. A. nilotica alone and as a constituent of CFB produced higher total gas but with lower methane while the partitioning factor (PF) was higher in Z. nummularia and its CFB. Substrate digestibility (both DM and OM) was lower (P < 0.001) in Z. nummularia compared to other forages and CFBs. The fermentation metabolites showed a different pattern for forages and their CFBs. The forages showed higher TCA precipitable N and lower acetate: propionate ratio in Z. nummularia while the related trend was found in CFB with V. sinensis. Total volatile fatty acid concentration was higher (P < 0.001) in A. nilotica leaves than V. sinensis hay and Z. nummularia leaves. It has implication on widening the forage resources and providing opportunity to use forage biomass rich in polyphenolic constituents in judicious proportion for reducing methane and enhancing green livestock production. CONCLUSION: Above all, higher substrate degradability, propionate production, lower methanogenesis in CFB with A. nilotica leaves may be considered useful. Nevertheless, CFB with Z. nummularia also proved its usefulness with higher TCA precipitable N and PF. It has implication on widening the forage resources and providing opportunity to use polyphenol-rich forage biomass for reducing methane and enhancing green livestock production.