Effect of inclusion level of selected enzymes and enzyme combinations on in vitro digestibility of maize (Zea mays) stover
This study examined the impact of varying dosages of cellulase, xylanase, and cellulase-xylanase (CX) combinations on in vitro dry matter digestibility (IVDMD), organic matter digestibility (IVOMD), and neutral detergent fibre digestibility (IVNDFD) of maize stover. In the first in vitro trial, cellulase and xylanase were added individually to ground maize stover at increasing rates of 0 (control), 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, and 6.5 g/kg DM. The best (based on IVNDFD) individual doses of 1.5 and 2.5 g/kg DM for cellulase and 2.5, 3.5, 4.5, 5.5 g/kg DM for xylanase were selected for the second in vitro trial to study the effect of combining the different levels of cellulase and xylanase on in vitro digestibility of maize stover. An increase (p<0.05) in IVNDFD was observed when increasing the dosage of cellulase from 0.5 to 2.5 g/kg DM (34.58 to 40.4%, respectively), thereafter, a decrease (p<0.05) from 38.0 to 33.2% was observed at 3.5 to 6.5 g/kg DM, respectively. Supplementing with cellulase in smaller doses of 1.5 and 2.5 g/kg DM yielded higher IVNDFD of 39.46 and 40.40%, respectively. Xylanase improved (p<0.05) IVOMD of maize stover across all graded levels compared to the control. There were no differences (p>0.05) in IVNDF digestibility when xylanase was applied at lower doses of 0.5 to 2.5 g/kg DM (ranging from 30.48% to 32.36%) and the highest dose of 6.5 g/kg DM (30.74%). The combination of different doses of cellulase and xylanase (CX) improved (p<0.05) IVDMD when compared to the control. In vitro dry matter digestibility (IVDMD) ranged from 51.18 % at CX 2.5 x 5.5 g/kg DM to 60.04% at CX 1.5 x 2.5 g/kg DM, with the negative control at 42.87%. The combination of cellulase and xylanase at lower levels of 1.5 g/kg DM and 2.5 g/kg DM, respectively, improved (p<0.05) the digestibility of DM, OM and NDF compared to when the enzymes were applied singly. In light of this investigation, it can be concluded that the enzyme, enzyme dosage, and enzyme combination all affect the digestibility of maize stover, with effective digestibility of maize stover achieved when cellulase and xylanase were combined at 1.5 and 2.5 g/kg DM, respectively.
Key words: maize stover, exogenous fibrolytic enzymes, enzyme dose, synergistic effect
