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The objective of this study was to evaluate the effect of correcting indigestible neutral detergent fibre (iNDF) for the loss of lignin in predictions of silage organic matter digestibility (OMD). Twenty-five primary and regrowth grass and red clover silages with known in vivo OMD in sheep were used. Silage and faecal samples were analysed by different lignin assays: the Klason method, acid detergent lignin (ADL) and permanganate lignin. The methods were evaluated by the Lucas test. The slopes in Lucas fits of primary and regrowth grass and red clover silages did not differ, and faecal recovery of ADL was not different from unity. The iNDF was recovered from 288-h in situ incubations in three dairy cows and analysed for ADL. Recovery of ADL in iNDF was 0·562 and 0·801 for grass and red clover silages. Silage concentration of iNDF performed better compared to the different lignin fractions in predicting OMD. Correcting individual samples for loss of ADL as well as using a general correction based on the Lucas fits of ADL in iNDF of grass and red clover silages lowered the prediction error of OMD, but despite losses of ADL in iNDF, the improvements in predictions of OMD were marginal.