Effects of Trace Mineral Source and Exogenous Enzymes on Ruminal in Vitro Fermentation of Roughage-Based or Concentrate-Based Simulated Diets

Two experiments evaluated the effect of trace mineral (TM) source (inorganic [ITM] and organic [OTM]) and 4 exogenous enzymes treatments [(1) control, without exogenous enzymes; (2) amylolytic enzyme [AMY; 1g of Amaize®/kg of substrate dry matter (DM)]; (3) fibrolytic enzyme (FIB; 2g of Fibrozyme®/kg of substrate DM; and (4) a multi-enzyme preparation (SSF; 2g of Allzyme® SSF/kg of substrate DM] on in vitro fermentation parameters of roughage-based or concentrate-based diets (Exp. 1 and 2, respectively). Two roughages were used in each experiment [high- and low-quality tropical grass hay in Exp. 1 (HQH and LQH, respectively), and corn silage and sugarcane bagasse in Exp. 2 (CS and SB, respectively)]. Each experiment was conducted as a randomized complete block (n = 3). Mixed ruminal microorganisms were incubated in anaerobic media containing 300mg of substrate diet and 50mL rumen fluid:buffer. Incubations were performed in batch cultures for 48h (Exp. 1) or 24h (Exp. 2) at 39°C. There were no three-way interactions observed for Exp. 1 or 2. Roughage × TM source interactions (P < 0.02) were verified for total gas production (GP), partioning factor (PF), methane (CH4) production and yield in both experiments. In Exp. 1, total GP of HQH and CS decreased about 18% with OTM (P < 0.02), while for LQH and SB they increased in the same proportion. The PF of HQH and CS were increased (P < 0.01), while LQH and SB decreased by 12% (P < 0.05) when OTM was added. The CH4 yield (mL/g DMd) decreased when LQH and SB were incubated with ITM (P < 0.02). The HQH have lower pH compared with the LQH (P < 0.001; 6.56 vs. 6.72). Additionally, PF presented TM source × enzyme interaction (P = 0.05). When ITM was included, PF was higher with addition of AMY than SSF (P = 0.04), but they were similar to CON and FIB. When OTM was supplemented, PF was greater with SSF compared with FIB (P = 0.04), but presented similar values to CON and AMY. In Exp. 2, GP was lower when SB and ITM was incubated together (P = 0.02; 141 vs. 175mL/g DM), while for CS there was no difference between ITM sources (P = 0.17). The CH4 yield reduced when OTM was combined with CS or when ITM was added with SB (P < 0.02). The PF of CS increased in 37% (P < 0.01), while SB decreased by 23% (P < 0.05) when OTM was added. As verified in Exp. 1, roughage affected pH and CS significantly reduced pH compared with SB (P < 0.001; 6.69 vs. 6.81). In conclusion, the in vitro treatment of substrates with different roughage-to-concentrate ratios with exogenous enzymes were minorly impacted by the TM source. The incubation of low-quality roughages with ITM source increased PF and decreased GP, which led to a consistent reduction in the CH4 yields. Additionally, IVDMD increased and lowered greenhouse gas production by OTM inclusion in high-concentrate substrate with CS, resulting in a favorable impact on rumen fermentation efficiency.