Insulin resistance (IR) is a problem in periparturient dairy cows. Chromium has the potential for lowering plasma free fatty acids and cholesterol concentration and IR. The role of chromium is probably associated with increasing the insulin internalisation and amplifying insulin signaling through activation of cellular insulin receptors. Chromium supplementation in the diet may have effects on microbial fermentation in the rumen. The aim of this study was to evaluate the effects of dietary chromium sulphate supplementation on microbial fermentation rate using an in vitro gas production method. Two fistulated beluchi sheep were sampled for rumen fluid. The basal diet for the gas production test was mixed with 0, 50, 100 and 200 ppm of chromium as chromium supplement. Feed samples were milled (1-mm screen). Gas production was recorded at various times up to 72 h of incubation with four replicates. The degradable parameters of DM were determined using the equation of P=b(1-e-ct) with P = accumulative gas production during time t; b = produced gas from fermentable fraction; c = gas production constant rate and t = time of incubation. There were no significant differences among treatments for c. The gas produced from fermentable fraction (b) of the 200 ppm Cr group was significantly (P<0.05) less than other treatments except 100 ppm group (0: 64.49±1.72a, 50: 65.83±1.49a, 100: 60.38±1.48ab, 200: 55.91±2.97b). This depression in gas production for concentration of 200 ppm may be the chromium toxicity in microbial environment. The results indicate that, based on in vitro measurements, chromium supplementation to a level of 100 ppm per diet has no reverse effects on microbial fermentation in the rume

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