Effects of an exogenous fibrolytic enzyme preparation on in vitro ruminal fermentation of three forages and their isolated cell walls

This study was completed to investigate whether a fibrolytic enzyme preparation with xylanase and cellulase activities (Fibrozyme™, Alltech Inc., Nicholasville, KY, USA), could stimulate in vitro rumen fermentation of alfalfa hay, grass hay and barley straw, and their isolated cell walls as neutral detergent fibre (NDF). Samples (500 mg) of each substrate were incubated in 120 ml bottles with 50 ml of buffered rumen fluid from sheep at 39 °C. The enzyme preparation was added directly to the bottles at the beginning of the incubation at levels of: 0 (control; CON), 50 mg/g substrate DM (LOWFIB) and 100 mg/g substrate DM (HIGHFIB). Effects on volatile fatty acid (VFA) production depended on substrate and incubation time. After incubation for 5 h, enzyme addition increased (P<0.05) production of VFA and acetate compared to CON for both alfalfa hay and its isolated cell wall, and increased (P<0.05) propionate and butyrate production in isolated cell wall, but reduced (P<0.05) them in alfalfa hay. After incubation for 10 h, addition of both doses of enzyme preparation increased (P<0.05) VFA and propionate production versus CON for both alfalfa hay and its isolated cell wall, and decreased (P<0.05) acetate to propionate ratios with both substrates, with intermediate values for LOWFIB and highest for HIGHFIB. After 24 h of incubation, there were no effects due to enzyme treatment or enzyme dose on rumen variables. Addition of both doses of supplemental enzyme increased (P<0.05) VFA, acetate and propionate production after 5 and 10 h incubation in both grass hay and its isolated cell wall, with increases being greater (P<0.05) for HIGHFIB versus LOWFIB in all variables. Both doses of enzyme addition reduced (P<0.05) the acetate to propionate ratio at 5 and 10 h of incubation. After 24 h of incubation, enzyme addition increased (P<0.05) VFA, acetate and butyrate production in both grass hay and its isolated cell wall versus CON, with some dose effects on both substrates. Enzyme supplementation also increased (P<0.05) VFA, acetate and propionate production versus CON in barley straw and its isolated cell wall at 5 and 10 h of incubation, with dose dependent effects after incubation for 5 h with higher (P<0.05) increases for HIGHFIB versus LOWFIB in both substrates. Both enzyme doses also reduced (P<0.05) the acetate to propionate ratio in both barley straw and its cell wall after incubation for 5 h. Production of total VFA and butyrate increased (P<0.05) with both doses of enzyme after incubation for 24 h. Final pH, ammonia-N and disappearance of aNDF and ADF did not differ among enzyme treatments after incubation of grass hay and barley straw or their isolated cell wall for 24 h. Results indicate that this fibrolytic enzyme preparation stimulated in vitro fermentation of substrates at short (5 and 10 h), but not at long (24 h) incubation times, and that effects depended on both the dose used and the presence of neutral detergent soluble components in the substrate.