Effect of fungal treatments of fibrous agricultural by-products on chemical composition and in vitro rumen fermentation and methane production

► A fungus-substrate interaction was observed on nutritional values of fibrous by-products. ► Nutritional improvement by some fungi linearly increased with the level of lignin in substrates. ► Pleurotus ostreatus is an effective lignin degrader but could not improve the nutritive value of fibrous by-products. ► Treatment of oil palm fronds with Ceriporiopsis subvermispora reduced methane emission from rumen fermentation.