Effect of tannin or inoculum as silage additives on silage quality and rumen fermentation kinetics

Abstract Text:

Tannin has the ability to bind with different compounds including protein and carbohydrate to form complex undegradable compounds. Tannin-protein complexes form in the rumen (pH 6-7) and disassociate in the abomasum (pH< 3.5) enhancing duodenal supply of dietary protein. The in vitro gas production technique can be used to predict rumen fermentation kinetics. The effect of additional tannin (hydrolysable, chestnut) and a bacterial inoculant as additives at ensiling on final silage quality and in vitro rumen fermentation kinetics were investigated. Whole crop grass, pea and bean forages were harvested on 07/14/2011 and ensiled in triplicate in experimental silos (25kg). Prior to ensiling each forage was treated with one of 4 additives: 40g/kg fresh weight (FW) tannin (HT), 20g/kg FW tannin (LT), an inoculant (L. plantarum) 10⁶ colony-forming units/g FW (In), or untreated (C). A standard volume of water (1 ml. /kg FW) was applied to all treatments.  Silos were opened after 100 days and subsamples stored (-20°C) prior to analysis for: pH, NH₃-N, DM, NDF, CP and water soluble DM component (WS). Rumen fluid was collected from four mature wethers (fitted with permanent rumen cannula) fed straw plus concentrates [80:20 DM basis] with ad libitum access to water. Gas production (in vitro) was measured as described by Theodorou et al. (1994) [J. Feed Sci. Tech. 48:185-197] and results fitted to an exponential decay curve (SigmaPlot12).  Duplicate samples were incubated for 72h with four experimental periods. The experiment was analysed as 3X4 factorial design using Genstat 15 (VSN International, UK).  The addition of tannin significantly reduced NH₃-N compared to control silages (41.60, 48.76, 55.66 and 60.01 g/kg total N for HT, LT, In and C respectively, SED=1.976, P<0.001). Moreover, both tannin levels reduced the WS compared to In and C (197.2, 235.4, 258.5 and 263.7 g/kgDM for HT, LT, In and C, SED=8.154 P <0.001). There was no significant effect (P>0.05) on other proximate analysis. Effect of additive on rumen fermentation kinetics for mean silages showed that additional tannin reduced the total gas pressure (300.3, 329.6, 370.1 and 375.1 kPa for HT, LT, In and C respectively SED=26.32, P<0.05) and the rate of fermentation (0.034, 0.037, 0.039 and 0.043, SED=0.0046, P<0.05) for HT, LT, In and C respectively. Addition of tannin at ensiling reduced crop protein degradation in silo and reduced rumen fermentation potentially increasing the supply of UDP to the small intestine.

Keywords: Tannin, silage, gas production