Abstract:

The experiment was conducted to study the effects of different surface tension (ST) of fermentation liquid and specific surface area (SSA) of neutral detergent fiber (NDF) on the processes of in vitro fermentation and to explore the mechanism. Three types of SSA (3.27, 3.73 and 4.44 m²·g^-1) of NDF distracted from rice straw, and four levels of ST (54, 46, 43 and 36 mN·m^-1) were assigned to a 3 × 4 factorial design. The samples were collected to determine the NDF disappearance rate, pH and ammonia nitrogen (NH₃-N) concentration at the fermentation time of 6, 12, 24, 36, 48 and 72 h, and to determine the total gas production at each fermentation time. The results as following: The gas production of fast and slow degradable fraction increased (P<0.001) with the decreasing of SSA of NDF particle. The NDF disappearance rate increased (P<0.001), but pH and the NH₃-N concentration decreased (P<0.001) as the increasing SSA of NDF. ST had significant (P<0.01) effect on gas production, pH and NH₃-N concentration and NDF disappearance rate. Gas production of fast fermentable parts and lag time significantly (P<0.001) decreased, but gas production of slow fermentable parts significantly (P<0.001) increased with the decreasing of ST, NDF disappearance rate had been prominently decreased (P<0.001), but the pH had been increased when ST below to 36 mN·m^-1. Those results indicate that substrate’s specific surface area and liquid surface tension directly influenced in vitro fermentation characteristics of fiber, and the rumen fermentation and feedstuff utilization could be regulated by adjust the SSA of substrate and the ST of rumen liquor.