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

Abstract

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 µg ml−1. Microbial incorporation of 15N was increased (P < 0.05) by 15 µg SAP ml−1 but decreased (P < 0.05) by 225 µg SAP ml−1. Gas and VFA production peaked with 75 µg SAP ml−1 and were elevated (P < 0.05) relative to control in the presence of 75 µg SAP ml−1. Microbial protein synthesis was increased (P < 0.05) by SAP at 15 µg 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 × diet interaction was recorded. The biological activity of YE was shown to be attributable to its SAP and to be diet-dependent. © 2000 Society of Chemical Industry. Contributions of Y Wang, T A McAllister, L J Yanke and Z Xu © Minister of Public Works and Government Services Canada 2000