The aim of the present study was to evaluate the effect of various non-fiber carbohydrates on gas production parameters of fibrous feeds [alfalfa hay (AH), wheat straw (WS) and cottonseed hulls (CH)]. Treatments were AH, WS and CH as non-supplemented or supplemented with glucose (GLU), fructose (FRU), sucrose (SUC) and starch (STA) used as 0.0, 30, 60 and 90 mg/g DM in a completely randomized design with a 3x4x4 factorial arrangement. In vitro gas production parameters of the treatments were determined (4 runs). Approximately, 0.3 g of each sample was placed in a 100 ml glass syringe containing 40 ml of buffered rumen fluid (ratio of buffer to rumen fluid was 2: 1). Rumen fluid was obtained from two rumen cannulated sheep (45.5± 2 kg, body weight) before the morning feeding and immediately strained through four layers of cheesecloth. Animals were fed with 1.5 kg DM alfalfa hay and 0.4 kg DM concentrates (165 g CP/ kg DM) per head per day. Syringes were incubated at 39 ºC and the volume of gas produced was recorded at 2, 4, 8, 12, 24, 36, 48, 72 and 96 h. The gas production data were fitted to an exponential equation of P= b (1 -e-ct), where b is the volume of gas produced, c is the fractional rate constant of gas production (/h), t is the incubation time (h) and P is the volume of gas produced at time t. Statistical analysis was conducted using SAS procedure. Supplementation of AH, CH and WS with each source of NFC, particularly as 60 and 90 mg/g DM, caused to increase the volume of gas produced (b) significantly (P< 0.05). Supplementation of AH with the source of NFC used in this study as 60 and 90 mg/g DM increased significantly (P< 0.05) the fractional rate constant of gas production ranged from 11 to 33%. When wheat straw was supplemented with FRU as 60 and 90 mg/g DM and SUC as 60 mg/g DM the parameter of (c) was significantly (P< 0.05) increased from 0.024 to 0.030, 0.031 and 0.029, respectively. Supplementation of CH with FRU and SUC as 30 mg/g DM caused to decrease significantly (P< 0.05) the c parameter from 0.017 to 0.010 and 0.011, respectively. It might be concluded that each source of NFC evaluated in the present study caused unique pattern of fermentation when added to a fibrous material.

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