Effects of trace mineral source and exogenous enzymes on ruminal in vitro fermentation of grazing and feedlot cattle diets

Abstract

Two experiments evaluated the effect of TM source (inorganic [ITM] and organic [OTM]) and 4 exogenous enzymes treatments [(1) control, without exogenous enzymes; (2) amylolytic enzyme (AMY; 1 g of AmaizeTM/kg of substrate DM; (3) fibrolytic enzyme (FIB; 2 g of Fibrozyme®/kg of substrate DM; and (4) a blend of exogenous enzymes (ALL; 2 g of Allzyme® SSF/kg of substrate DM] on in vitro fermentation parameters of 2 contrasting diets (65:35 and 15:85 roughage-to-concentrate ratios at 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 300 mg of substrate diet and 50 mL buffer solution. Incubations were performed in batch cultures for 48 h (Exp. 1) or 24 h (Exp. 2) at 39°C. There were no three-way interactions at the Exp. 1 and 2. A roughage × TM source interactions (P < 0.02) were verified on GP, PF, CH4 production and yield in Exp. 1 and Exp. 2. 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. In an opposite way, partitioning factor (PF; an indicator of fermentation efficiency) of HQH and CS were improved (P < 0.01), while for LQH and SB decreased in about 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), and, in Exp. 2, also reduced when OTM was combined with CS (P < 0.05). There were no effects of treatments and interactions (P > 0.08) on total VFA. As expected, roughage affected pH; HQH and CS significantly reduced pH compared with the LQH and SB (6.56 vs. 6.72 and 6.69 vs. 6.81 in Exp. 1 and Exp. 2, respectively; P < 0.001). Additionally, PF presented TM source × enzyme interaction (P = 0.05) in Exp. 1. When ITM was included, PF was higher with addition of AMA than ALL (P = 0.04), but they were similar to CON and FIB. When OTM was supplemented, PF was xii S enhanced with ALL compared with FIB (P = 0.04), but presented similar values to CON and AMA. In conclusion, the in vitro treatment of substrates with different roughage-toconcentrate ratios with exogenous enzymes were little impacted by the TM source. The incubation of high-quality roughages with OTM supplementation promoted an increase in PF and decrease GP, led to a consistent reduction in the CH4 yields. Thus, it seems that OTM supplementation must be prioritized in systems which use high-quality tropical roughages.