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Aims: To determine nutritive value of rice straw samples biodegraded by different fungal strains.

Study Design: Completely Randomized Design.

Place and Duration of Study: Fungal inoculation of rice straw samples was carried out at the Federal Institute of Industrial Research Oshodi (FIIRO) Nigeria, for 21 days; proximate and fibre fractions analysis was done at the laboratory of the International Institute for Tropical Agriculture (IITA) Ibadan, Nigeria, while in vitro gas production was carried out at the laboratory of the Department of Animal Science, University of Benin, Nigeria.

Methodology: Samples of untreated rice straw (UTRS) were biodegraded for 21 days using three strains of edible mushroom Pleurotus tuberregium (PTTRS), Pleurotus pulmonarius (PPTRS) and Pleurotus ostreatus(POTRS). The substrates were analyzed for changes in the proximate composition and crude fibre fractions. In vitro Gas Production (IVGP) was used to predict the Metabolizable Energy (ME), Organic Matter Digestibility (OMD), Short Chain Fatty Acids (SCFA), methane production (CH4), gas production at zero hour (a), total gas production (b), rate of fermentation (c) and incubation time (t).

Results: Proximate composition showed crude protein (CP), ether extract (EE), ash and nitrogen free extracts (NFE) values to be 8.32,15.32, 5.95 and 6.44%; 2.91, 3.93, 3.43 and 1.90%; 5.88, 12.38, 7.26 and 13.76% and 48.75, 43.65, 46.51 and 27.40% for UTRS, PTTRS, PPTRS and POTRS respectively. Crude fibre fractions for neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), hemicellulose (HEM) and cellulose (CL) were 72.06, 77.43, 73.71 and 76.63%; 51.31, 6.14, 12.44 and 10.87%, 11.39, 1.43, 1.23 and 1.37%; 20.75, 71.29, 61.27 and 65.77% and 39.92, 4.71, 11.22 and 9.49% for UTRS, PTTRS, PPTRS and POTRS respectively. Estimates of ME, OMD, SCFA and CH4 were 4.23, 7.29, 7.32 and 9.10 MJ/kg DM; 31.34, 52.94, 45.39 and 57.83%; 0.18, 0.56, 0.56 and 0.78 umol/200 mg DM and 13.50, 9.33, 10.33 and 10.67 ml for UTRS, PTTRS, PPTRS and POTRS respectively. IVGP characteristics for a, a+b, b, c and t were 1.25, 2.38, 1.13 and 1.57; 9.25, 23.88, 24.13 and 24.07; 8.00, 21.50, 23.00 and 22.50; 0.11, 0.41, 0.35 and 0.35 and 21.00, 8.00, 9.00 and 9.00 hours for UTRS, PTTRS, PPTRS and POTRS respectively

Conclusion: Based on the result, Pleurotus tuberregium degraded rice straw (PTTRS) was adjudged superior to the others due to the higher crude protein, ether extract, potentially degradable fractions, high gas production per unit time and lower methane production.