Effect of the method of preservation on the chemical composition and in vitro fermentation characteristics in two legumes rich in condensed tannins

The objective of the present study was to evaluate the effects of preservation (hay and silage) on the chemical composition and the in vitro fermentation characteristics in comparison with fresh forage in two legumes rich in condensed tannins (CT). Sainfoin (Onobrychis viciifolia) was collected at the late bloom stage and sulla (Hedysarum coronarium) at the early bloom stage. In each forage, a part was immediately freeze-dried, a part was dried at ambient temperature to obtain hay, and another part was ensiled in vacuum-packages for 82 days. An in vitro assay to study the fermentation was carried out with an Ankom system during 72 h. In both forages, the silages had different contents of polyphenols and condensed tannins fractions than fresh forage and hay (P<0.05). Sainfoin hay only had greater content of fibre-bound CT fraction (FBCT) than fresh sainfoin, whereas sulla hay had greater protein-bound CT and FBCT contents than fresh sulla (P<0.05). Sainfoin silage had lower gas and methane production than hay and fresh forage (P < 0.001), whereas fresh sulla had greater gas and methane production, followed by hay and silage, which produced the least (P<0.05). In both legumes, hay had lower in vitro organic matter digestibility (IVOMD) than silage and fresh forage (P<0.001). The method of preservation affected the total production of volatile fatty acids (VFA) only in sulla (P<0.05). Most of the proportions of individual VFA were affected by the method of preservation in both legumes (P<0.001). In conclusion, polyphenols content, total content and fractions of CT were more affected in the silages than in the hays when compared to fresh forages. However, according to gas and methane production and IVOMD, silage may have greater feed nutritive value than hay although further studies on animal performance are warranted before recommendation.