The objective of the present study was to evaluate the effect of cumin essential oil (CEO) on in vitro gas production parameters of alfalfa hay (AH), barley grain (BG) or sugar beet pulp (BP). Samples of AH, BG, and BP were provided as untreated or treated with CEO (400 mL/g DM). In vitro incubations were carried out using 0.3 g of each sample (4 replicates) which was placed in a 100 mL glass syringe containing 40 mL buffered rumen fluid (ratio of buffer to rumen fluid was 2:1). Rumen fluid was obtained from 2 ruminally cannulated sheep (body weight = 45.5 ± 2 kg), before the morning feeding, and immediately strained through 4 layers of cheesecloth. Animals were fed 1.5 kg DM alfalfa hay and 0.4 kg DM concentrate (165 g CP/ kg DM) per head per day. Syringes were then incubated at 38.6°C and the volume of gas produced was determined at 2, 4, 8, 12, 24, 36, 48, 72 and 96 h after the incubation. The gas production data were fitted using 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 (1999) software. Results demonstrated that the gas production parameters of the feed samples (Table 1) were significantly different (P < 0.05). In addition, results of the present study indicate that the gas production parameters of the feed samples were significantly altered when CEO was included in the medium. Cumin essential oil caused a significant (P < 0.05) decrease of c parameter of BG and BP. While, when cumin was added to the AH and BP samples, the b parameter was decreased (Table 1).

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