Effects of hydrolysable tannin extract and dry matter concentration on ensiled legume and grass forages – Chemical composition, crude protein fractions and in vitro gas production kinetics

Abstract

Pre-ensiling treatments can have a distinct impact on crude protein (CP) degradation and fermentation characteristics of ensiled high-protein forages. The objective of this study was to investigate the effects of different dosages of chestnut tannin (CT) and dry matter (DM) concentration on chemical composition, nitrogen (N) compounds as well as in vitro gas production (GP) in grass and legume silages. Pure stands of lucerne (Medicago sativa L.), Italian ryegrass (Lolium multiflorum L.) and red clover (Trifolium pratense L.) were harvested and wilted to DM contents of approximately 200 and 350 g/kg. The forages were then ensiled in 120-litre barrels with three levels of hydrolysable tannin (HT) supplementation (0, 20 and 40 g/kg DM). After ensiling, six silage treatments of each forage species were sampled for chemical analysis, particularly with regard to proximate constituents, fermentation products and other volatile compounds, CP fractions and 96-h in vitro gas production (GP) characteristics. In order to statistically evaluate the effects of HT and DM treatments, data were analysed using analysis of variance as well as orthogonal contrast test (linear and quadratic). In addition, the mean GP kinetics over time were estimated using nonlinear regressions. The stepwise increase of HT concentration linearly reduced the accumulation of non-protein-N (NPN) in all forages (P < 0.01) by at least 20 % in low DM silages and by 10 % in silages with a higher DM level. Both, HT and DM treatments resulted in a significant decrease (P < 0.05) of ammonia-N concentration. Among all forage species, the extent of proteolytic activities was highest in untreated low DM lucerne silages, as NPN and ammonia-N concentrations were 824 g/kg CP and 198 g/kg N, respectively, whereas the lowest CP degradation was generally determined in red clover silages. Maximum GP as well as organic matter digestibility (OMD) were negatively affected by increasing HT dosage in all forage species (P < 0.05), with the impact being more pronounced in moister silages. On the other hand, wilting to a higher DM content increased GP and OMD in red clover and Italian ryegrass silages. The present study revealed that HT markedly improved CP quality in silages due to higher stability of protein, whereas the DM treatment had more beneficial effects regarding fermentation quality, OMD and GP.