The effect of microwave irradiation on in vitro gas production kinetics of linseed was investigated. Samples were milled (I mm). then exposed to a 2.450 MHz continuous microwave radiation by an average specific absorption rate (SAR) of75.5 W/kg for 0.0 (CON), 10,30,60,120 or 150 seconds. Approximately 500 mg of oven dried sample was incubated with 50 ml buffered rumen fluid (ratio of buffer to rumen fluid was 2: I) in a 125 ml glass bottle (n=9) at 38.6 °C using water bath for 2, 4, 6, 8, 12, 24, 48 and 72 h. Cumulative gas production values were corrected for blank incubation and fitted to an exponential equation Y=b( I_e-(ct-I)),where b is the gas production from the fermentable fraction (ml), c is the gas production rate constant for b, t is the incubation time (h), I is lag time (h) and Y is the gas produced at time t. Data were analyzed using the GLM procedure of SAS 9.2 and the means were compared by the LSD test (P<0.05). The amount of gas produced from the fermentable fraction (b :I:SE) was 53.3b:l:O.83, 48.4c:l:O.88. 56.4\":1:1.59. 42.9d:l:O.97, 31.8f:l:I.08 and 37.0.:1:0.78 ml; The fractional constant rate (C:l: SE) was 0.058a:l:O.0024, \" 0.055\":1:0.0025. 0.044b:l:O.0028, 0.05Iab:l:O.0026. 0.045b:l:O.0034. 0.046b:l:O.002 h; and the lag time (I :I: SE) was 0.7c:l:O.19, l.4b:l:O.19, 1.6b:l:O.28,2.8\":1:0.19, 2.6\":1:0.29, 2.7\":1:0.18 h for 10, 30, 60, 120 and 150 s. respectively. Irradiation for 30 s caused to increase the amount of gas produced significantly (P<0.05) from the fermentable fraction (b) compared with CON. Irradiation for 30, 120 or 150 s decreased the fractional constant rate (c) of the samples than that of the CON. Furthermore. irradiation significantly increased fermentation lag time (P<0.05). Results indicated that the microwave irradiation for more than 60 s might significantly reduce both band c parameters and could increase fermentation lag time. Session

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