This experiment aimed to investigate the effects of level of Natuzyme@ (Bioproton Co.) on in vitro gas production (GP, ml/200 mg DM), dry matter disappearance (IVDMD) methane production (MET, ml/200 mg OM) and fermentation efficiency as mg IVOMO per mlMET (FE) of various ruminant diets containing wheat straw (DI: 6.2% wheat straw, 39.4% corn silage) or alfalfa hay (02: 21.3% alfalfa, 37.2% corn silage) at half time (tl 12)of gas production. Approximately, 200 mg (OM) of each diet was weighted in a 125ml serum bottle. while 24 h prior to incubation each bottle received 0.84, 1.68and 2.52 glkg OM of the enzyme (E I, E2 and E3, respectively) in an aqueous suspension to maintain same moisture content (40%). run=3 and n=3. The gas production procedure was followed by pipetting buffered rumen fluid into the bottles and incubated at 38.6 °C for desired intervals. In a pre-trail, pressure of gas was recorded at 2, 4, 6, 8, 10, 12, 24. 48, 72 and 96 h of incubation. Pressure data was converted to volume using an experimental curve and was modeled to estimate t1/2. Main trail incubation was continued until tl/2 and volumes of GP and ME, and residual OM was measured. Data were analyzed as 3x2 factorial arrangement in a completely randomized design. Results showed that 01 compared with 02 had higher FE (6.77 vs. 5.59), less GP (33.68 vs. 35.71) and MET (9.20 vs. 10.87), (P<0.05). In addition. both E2 and E3 compared with El had significantly (P<0.05) higher GP (36.70 and 36.75 vs. 30.63) and MET (10.81 and 10.39 vs. 8.91). The IVOMO was significantly (P<0.05) higher in E3 than those of the El and E2 (33.90 vs. 27.90 and 28.40. respectively). It seems that combination of improved IVOMO and FE using E3 comparing with El and E2 could be advantageous but the outcome can vary considering type and forage content of diet.

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