In vitro study of the effects of condensed tannins in sainfoin on the digestive process in the rumen at two vegetation cycles

One approach to reducing enteric production of greenhouse gases (GHG; i.e. , nitrous oxide and methane) is to feed tanniniferous forage plants such as sainfoin. The objective of this study was to investigate, in vitro , effects of the content and structural characteristics of condensed tannins (CT) in the whole plant, leaves and stems of sainfoin ( Onobrychis viciifolia ) on the digestive process in the rumen. Sainfoin, studied during the first vegetation cycle at the end of flowering, and during the second vegetation cycle at the start of flowering, was incubated in serum bottles containing buffered rumen fluid for 3.5 and 24 h. To assess effects of CT, incubations were with and without added polyethylene glycol (PEG), to neutralise CT effects. Biological activity and prodelphinidin (PD) content were higher (P cis value was lower (P 4 values for stems and leaves at two vegetation cycles (P 2 :CH 4 ratio was lower (P 4 production, or the CO 2 :CH 4 ratio, at either 3.5 or 24 h of incubation. At both incubation periods, in vitro true organic matter digestibility (IVTOMD) was higher for leaves than stems (P 3 –N for leaves and stems in both vegetation cycles. For the whole plant, PEG resulted in higher NH 3 –N content (P 4 production without altering its organic matter digestibility and N value, but research on the nutritional impact of CT must not only be based on CT content in plant tissue, but include structure-activity considerations of CT.