Influence of different morphological parts of buckwheat (Fagopyrum esculentum) and its major secondary metabolite rutin on rumen fermentation in vitro

It was hypothesized that buckwheat, especially its flowers, influences foregut fermentation in ruminant animals because it is rich in phenolic compounds. The entire fresh aerial buckwheat herb, or its parts (leaves, stems, flowers and grain), were incubated for 24 h together with pure ryegrass (1:1, dry matter basis) in an in vitro ruminal fermentation system (Hohenheim Gas Test). Additionally ryegrass, supplemented with 0, 0.5, 5, or 50 mg rutin trihydrate/g dry matter, was incubated. Contents of extractable phenols (g/kg dry matter) were the highest in buckwheat flowers (88), followed by leaves (63), and the lowest in ryegrass (8). The levels of production of total gas and volatile fatty acids demonstrated that the nutritional value of buckwheat was slightly lower than that of ryegrass. Compared to ryegrass alone, ruminal transformation of dietary protein-N into ammonia was lower with 50 mg rutin, buckwheat flowers and buckwheat leaves. Thus, these treatments appeared to have partly protected dietary protein from ruminal degradation. Rutin, at the highest level, buckwheat flowers and the total aerial fraction of the buckwheat plant suppressed methane per unit of total gas by > 10%, either at elevated (rutin) or reduced total gas volume. This indicates that the ways of the influence on the ruminal fermentation pattern differed between pure rutin and buckwheat. In vivo studies have to confirm these potentially beneficial effects of buckwheat if used as forage for ruminants and clarify the role of further phenolic compounds present in buckwheat. Abbreviations: DM = dry matter, HGT = Hohenheim Gas Test, NDF = neutral detergent fibre, TEP = total extractable phenols, VFA = volatile fatty acids