In vitro effects of steroidal saponins from Yucca schidigera extract on rumen microbial protein synthesis and ruminal fermentation

In a first experiment, ground alfalfa hay and rolled barley grain were incubated in buffered ruminal fluid with and without Yucca schidigera extract (YE, 0 or 10 mg ml(-1)). Gas and total VFA production from barley grain were increased (P < 0.05) by YE during the first 10 h of incubation; from alfalfa hay, these were reduced (P < 0.001) throughout the 24 h. Yucca extract reduced (P < 0.001) acetate/propionate ratios and ammonia concentrations, irrespective of substrate, In a second experiment, ground barley grain was incubated in a buffered suspension of mixed ruminal microbes obtained by low-speed centrifugation of ruminal fluid. Steroidal saponins (SAP) isolated from YE were included at 0, 15, 75 or 225 <mu>g ml(-1). Microbial incorporation of N-15 was increased (P < 0.05) by 15 <mu>g SAP ml(-1) but decreased (P < 0.05) by 225 pg SAP ml(-1). Gas and VFA production peaked with 75 <mu>g SAP ml(-1) and were elevated (P < 0.05) relative to control in the presence of 75 <mu>g SAP ml(-1). Microbial protein synthesis was increased (P < 0.05) by SAP at 15 <mu>g ml(-1) and reduced (P < 0.05) by the higher concentrations. Acetate/propionate ratios were linearly reduced by SAP from 8 to 24 h incubation (P < 0.01). The effects of SAP on digestive microbes were less pronounced (P < 0.05) with barley grain digestion than with alfalfa. A YE x diet interaction was recorded. The biological activity of YE was shown to be attributable to its SAP and to be diet-dependent. (C) 2000 Society of Chemical Industry. Contributions of Y Wang, TA McAllister, LJ Yanke and Z Xu (C) Minister of Public Works and Government Services Canada 2000.