Chopped and pressure-pasteurized wheat straw in the form of compost was seeded with mushroom mycelium. Chemical composition, ruminal disappearance and in vitro gas production were carried-out on the samples taken on day 0, 21, 42, 63 and 84 after seeding. NDF, ADF and Lignin content of the treated wheat straw reduced significantly with a rate of 0.20, 0.10 and 0.04% per day. Crude protein content increased significantly from 46.6 g kgG on day 0-50.90 g kg1 G1 on day 84. The a fraction for dry matter was highest (p<0.05) for the straw under the mushroom growing conditions (e.g., 0.188 g gG1 for the day 0 and 0.342 for the day 84). In contrast, the b value significantly (p<0.05) reduced from day 0-84 (0.487 and 0.336 g gG1). The value for crude protein and NDF parameters increased linearly with increasing the growing period. Generally, the ruminal disappearance of different nutrients increased by growing the Pleurotus ostreatus, although, the c rate was independent. In case of gas production, mushroom growing led to a significant more gas production during the early hours (less than 24 h) of incubation. The b fraction of in vitro gas production as well as in situ results reduced significantly from day 0-84. It was concluded that straw seeding with P. ostreatus can be more effective for the longer period of growth.

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