In vitro evaluation of the effect of exogenous lignolytic enzymes on the nutritive value of Eleusine coracana (ragi straw)

Crop residues are renewable sources of energy for ruminants. Pre-digestion of such materials with ligninases from white rot fungi may transform the lignocellulosic substrate into a feed with greater digestibility and higher quality for ruminants. This study has evaluated the effect of different doses of three exogenous lignolytic enzymes -laccase (Lac), lignin peroxidase (LiP) and manganese peroxidase (MnP) obtained from immobilized Pleurotus flabellatus, Poria placenta and Coriolus versicolor (Polystictus versicolor) on the nutritional profile and in vitro digestibility of ragi straw. P. plascenta recorded the highest activities of laccase and lignin peroxidase of 270.23 ± 8.90 and 182.11 ± 10.47 U mg⁻¹ respectively and C. versicolor recorded 257.23 ± 5.38 and 163.20 ± 12.93 U mg⁻¹ of laccase and lignin peroxidase activity. The activities of these two lignolytic enzymes were lower (P<0.05) in Pleurotus flabellatus, which had the highest activity of Mn Peroxidase (63.54 ± 1.98 U mg⁻¹). Ragi straw of 2.3 to 3.0 cm length was supplemented as well as treated for 24 h by spraying with this enzyme rich media harvested from each individual fungi at varying ratios of 1:5; 2:5 and 3:5. No significant changes (p>0.05) were obtained either in cell wall components (NDF, ADF ADL) or the in vitro digestibility in any of the fungi upon supplementation with the lignolytic enzymes. Upon treatment with lignolytic enzymes of Coriolus versicolor at a ratio of 2:5, there was an increase in the protein and NDF contents (5.29 ± 0.62 and 61.77 ± 1.99) when compared with the untreated straw (3.74 ± 0.95 and 70.20 ± 5.8). The increase was significant (p < 0.05). With the treatment, the ADF and ADL were 30.84 ± 2.12 and 5.62 ± 0.06 respectively. The digestibility of the untreated straw was 40.0 ± 3.65, whereas the in vitro dry matter digestibility of ragi straw treated with C. versicolor was higher (49.03 ± 3.24%) with significance (p < 0.05) and with P. flabellatus it was 48.23 ± 1.06%. Enzyme treatment at a ratio of 2:5 was shown to be beneficial in all the fungi tested. However, further studies in vivo are warranted to corroborate the findings of this study