Aims: To evaluate the in vitro effect of an exogenous commercial enzyme blend (Natuzyme®) on fermentation responses and methane production of corn silage based diet. Study Design: Completely randomized design. Place and Duration of Study: Department of animal science, Faculty of agriculture, Ferdowsi University of Mashhad, between November 2012 and March 2013. Methodology: Two hundred fifty mg of milled and dried corn silage based diet in 3 runs and four replicates was weighed into 125-ml serum bottles for an in vitro gas production trial. A solution of a commercial enzyme blend (Natuzyme®) was added 12 hour prior to commence of the incubation (96 h) to make treatments of 1.68 and 2.52 (g/kg). No added enzyme bottles were considered as control. Gas production parameters at 96 h incubation were estimated and half time of gas production (t1/2) was calculated. Another gas test was run according to t1/2. All the incubations for each treatment were terminated at t1/2 and gas and methane volume recorded. Apparent dry matter degradability was assessed by centrifugation and ml methane per mg dry matter apparently degraded was calculated. Results: Gas production parameters were not affected by addition of the enzyme blend. Supplementation of a corn silage based diet with the enzyme as 1.68 or 2.52 g/kg dry matter of the diet increased apparent dry matter degradability by 21% compared with control. Gas production, methane volume and volume of methane per mg of dry matter apparently degraded were not influenced by incrementing level of Natuzyme®. Conclusion: Natuzyme® at the doses applied in the current experiment was capable of improving apparent dry matter degradability of corn silage based diet.

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