Evaluation of the efficacy of varying xylanase to cellulase ratio on ruminal fermentation of untreated and alkali treated oat straw

Abstract

Abstract Two in vitro ruminal fermentation assays were conducted to study the effect of exogenous fibrolytic enzyme (EFE) supplementation on untreated and alkali treated oat straw. During the first experiment, five CellulasePLUS-XylanasePLUS (DyadicPLUS International Inc.) complexes (EFE): DEF1 (100% CellulasePLUS), DEF2 (100% XylanasePLUS), DEF3 (50% CellulasePLUS + 50% XylanasePLUS), DEF4 (75% CellulasePLUS + 25% XylanasePLUS), DEF5 (25% CellulasePLUS + 75% XylanasePLUS) at varying xylanase to cellulase ratio (between 0.49 and 2.2) were assessed at 0, 0.5, 1, 2, 3, 5, 10, 20, 30 µl/gDM. DEF1 and DEF2 were subject to higher doses 60 and 100 µl/g DM. 200 mg of grounded oat straw was anaerobically incubated with buffer solution, fresh ruminal fluid, and EFE. The gas production (GP) was measured during 96h of incubation. EFE supplementation improved the rate and extent of GP and exerted quadratic responses (p-value < 0.001) for most parameters. The highest results were recorded for DEF3 (xylanase to cellulase = 1.5) with its optimal dose D5 = 5µl/gDM. As compared to the control, DEF3 increased the GP, GP rate, OMD, VFA and ME by 63.7%, 144.7%, 77.2%, 135.5%, and 54.8%, respectively. The responses to EFE were dependent on dose rate and varying xylanase to cellulase ratio. DEF3 was reevaluated in second experiment on untreated, NaOH (OSS) and Urea (OSU) treated oat straw. DEF3 was less effective regarding GP, fermentation parameters, and estimated OMD, ME, and VFA of OSS and OSU. Therefore, selecting the best xylanase to cellulase ratio and its optimal dose depends on chemical composition of the targeted substrate because of enzyme-substrate specificity.