Influence of formic acid and dry matter on protein degradation in the tanniniferous legume sainfoin

Improved protein utilization due to protein tannin binding has been observed in sainfoin and other tannin containing legumes. Since it is well known that binding of protein to tannins and dissociation of the resulting complexes are pH dependant, effects of low pH after treatment with unusually high amounts of acidic silage additives and different dry down stages on fresh herbage prior to ensiling was investigated. Criteria for tannin binding effects were based on N fractionation in an in vitro ruminal digestion system. A mixture of sainfoin varieties were wilted to different dry matter (DM) levels and treated with 0, 4 and 8 ml formic acid per kg fresh matter prior to ensiling for 60 days. Nitrogen fractionation included measurement of total N, buffer soluble N, non-protein N, α-amino acid N and ammonia N. Protein degradation was measured by an in vitro ruminal protein digestion system. Results show beneficial effects of moderate and high acidification particularly for buffer soluble N at 180 and 400 g/kg DM (P<0.0001) while these effects level off at 500 and 600 g/kg DM (P<0.852). However, no negative effect related to impaired tannin protein binding in the silages or the in vitro protein degradation occurred.