The stability of the gut ecosystem, especially the rumen, is an important area of research that has an impact on the use of feed additives and is associated with a number of diseases. The current study aimed to survey the effect of concentrate: roughage (C: R) ratio and the addition of kefir on the production characteristics of in vitro ruminant fermentation. In a 5x6 factorial order, six ratios of C: R (100:0, 80:20, 60:40, 40:60, 20:80 and 0:100) and five doses of kefir (0, 0.8, 1.6, 2.4, and 3.2 ml) were used, respectively. Gas production during incubation was estimated at 0- 96 h. During inoculation, the rumen fluid was obtained at 0, 4, 8, 12, and 24 h of incubation. Cumulative gas production, GPDM, GPOM, and GPNDF at 24 h was highest at the C: R ratio of 100:0 (67.82 mL, 75.92 mL/ 200 mg, 1979.15 mL/200 mg, and 11.11 mL/ 200 mg, respectively). The kefir addition improved the kinetics and gas production significantly. The highest in vitro dry matter and organic matter digestibility (IVDMD and IVOMD) were obtained at the C: R ratio of 100:0 (9.26% and 182.2% higher than those in C: R ratio of 0:100, respectively). The increase of concentrate diet ratio improved the overall volatile fatty acids (TVFA). No interaction effect on the gas production was detected between the C: R ratio and kefir. The microorganism populations were influenced neither by the level of concentrate nor by the level of kefir. Consequently, the high concentrate-to-roughage ratio and the addition of 1.6 mL kefir to the overall dietary substrate could promote rumen fermentation and feed digestibility without affecting microbe counts.
Keywords: Concentrate; Gas production; In vitro ruminal fermentation; Kefir; Roughage.