The effects of pre-treating different types of roughages with alkali on the efficacy of exogenous fibrolytic enzymes for improving their digestibility were studied in vitroin factorial arrangement 4 × 3 × 5 (enzyme, treatment and roughage types). Two fibrolytic feed enzymes novozyme (N) and celloclast (C) their combination (N+C) were evaluated for their potential to improve in vitrodegradation of different roughages including two straws (wheat straw: WS; barley straw: BS), grass hay (GH), corn stover (CS) and corn cobs (CC) as untreated or alkaline treated (NaOH or urea). The enzyme products were in liquid form and applied at a rate of 1 mg enzyme protein/g DM substrate. Anaerobic buffer medium and strained ruminal fluid were added to the in vitroincubations. Degradabilities of dry matter (DM), neutral detergent fibre (NDF), cellulose, soluble protein and reducing sugar profiles were determined at the end of the 24 h incubation. Overall NDF degradability of roughages were slightly increased by alkaline treatment (P<0.05) but, the addition of fibrolytic enzymes directly to the ruminal fluid at the application rates could not increase significantly DM or cellulose degradation (P>0.05). Use of fibrolytic enzymes released higher amounts of reducing sugars and lower soluble protein compared to control (P<0.05). Alkali treatment increased (P<0.05) the degradability of DM and fiber degradability. It was higher in NaOH treated forage compared to urea treated forages (P<0.05). تفاصيل المقالة