In vitro evaluation of bulk and nanosized cumin (Cuminum cyminum) extract on rumen gas production kinetics, methane and carbon dioxide productions, nutrient degradability, and fermentation end-products

This study evaluated the effects of cumin ( Cuminum cyminum ) extract presented as a normal-sized bulk extract (CEB) or an oil-in-water nanoemulsion (CEN) at inclusion levels of 0, 15, 30, and 45 µL/g dry matter (DM) on in vitro rumen gas production (GP) kinetics, methane (CH 4 ) and carbon dioxide (CO 2 ) production, nutrient degradability, and rumen fermentation end-products. Treatment effects were evaluated in a completely randomized design with a 2 × 3 + 1 factorial arrangement using the gas production method. Both extract forms linearly increased ( P < 0.001) the asymptotic GP ( b ), fractional rate of GP ( c ), lag time, metabolizable energy (ME), and gas yield at 24 h (GY 24 ) in a linear dose-dependent manner, while the partitioning factor at 48 h (PF 48 ) declined. The CEN form produced significantly greater responses than the CEB form (Form P < 0.001 for all kinetic parameters). Methane productions expressed as a percentage of total GP were reduced linearly ( P < 0.001) by both forms, with the CEN at 45 µL/g DM achieving a 37.8% reduction relative to the control, compared with 26.7% for the CEB form. Carbon dioxide production per unit of DM increased substantially with the CEN. In vitro degradability of DM, neutral detergent fiber, and acid detergent fiber increased linearly ( P < 0.001) with both extract forms. Rumen pH declined linearly with increasing dose of both the CEB and CEN forms, reaching a minimum of 6.70 at CEN45, a value within the physiological range compatible with normal rumen function. The concentrations of total volatile fatty acids, acetate, propionate, and butyrate increased significantly ( P < 0.001) with the CEN, yielding concentrations up to 18.0% higher than the control. In contrast, the molar proportions of individual VFAs were altered, with a slight decrease in acetate and propionate proportions and an increase in butyrate proportion ( P ≤ 0.01). Ammonia–Nitrogen (NH 3 –N) declined with increasing extract concentration for both forms ( P < 0.001 for dose effect). These findings indicate that the CEN form produced more pronounced changes in gas production kinetics, nutrient degradability, and fermentation end-products than the CEB form, and that both forms decreased CH 4 as a proportion of total gas production without a corresponding reduction in absolute CH 4 output, indicating a shift in fermentation pattern rather than confirmed inhibition of methanogenesis. The nanosized form at 30–45 µL/g DM warrants further evaluation, pending in vivo validation, active-compound standardization, and assessment of nanoemulsion stability.