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The aim of this study was to compare the gas production profiles and nutrient degradability of two diets using automatic and semiautomatic in vitro gas production techniques. A randomized block design in a 2 × 2 factorial arrangement was adopted, with two diets comprising different proportions of nonfiber carbohydrates (NFCs) (low-NFC vs. high-NFC diets), two gas production measurement techniques (automatic vs. semiautomatic) and four replicates. The blocks represent three in vitro runs. Gas production from the fermentation of fiber carbohydrates (Vf2) was 22% higher when measured with the automatic technique than with the semiautomatic technique. The Vt of the low-NFC diet differed between techniques and was 22.9% higher using the automatic technique. A highly positive correlation (r = 0.96) was observed between the techniques, with a high coefficient of determination between the techniques (R2 = 0.93). There was greater degradability of dry matter (DMD) and organic matter (OMD) with the automatic technique. In both diets, the degradability of crude protein (CPD) was greater with the semiautomatic technique (p < 0.0001). The high-NFC diet resulted in a lower pH and lower NH3-N in the incubation medium than in that of the low-NFC diet, whereas the degradability of DM, OM and CP increased. The automatic and semi-automatic techniques similarly estimated the kinetic parameters and the profiles of total gas production, demonstrating the potential of both techniques for assessing the nutritional value of diets with different proportions of NFCs.