Effects of Yucca schidigera extract on fermentation and degradation of steroidal saponins in the rumen simulation technique (RUSITEC)

A rumen simulation technique (RUSITEC) apparatus with eight 940 ml fermentation vessels was used to study the effects of the steroidal saponins in Yucca schidigera extract (YE) on ruminal microbial activity and saponin degradation. The YE contained approximately 4.4% (w/w) saponin, as smilagenin equivalents, and was included at 0 (control) or 0.5 mg ml ^-1 (n=4) in the McDougall's buffer infused continuously into the vessels (dilution rate=0.75 day ^-1). Each vessel received 5 g chopped alfalfa hay and 5 g concentrate (as-fed basis) daily for 22 days. Ammonia concentrations were lower (P<0.05) in effluent from vessels receiving YE than from controls for the first half of the study, but did not differ thereafter. Total amounts of VFA in effluent were not affected (P>0.05) by YE, but molar proportions of iso-butyric and iso-valeric acids were lower (P<0.05) in the YE vessels than in the controls in the first half of the experiment. Yucca extract at 0.5 mg ml ^-1 did not affect (P>0.05) dry matter disappearance (DMD) from hay or from concentrate, nor did it affect total gas or methane production, or bacterial numbers (total or cellulolytic populations) in homogenates prepared from fermenter vessel liquid and feed particles. Protozoal numbers in the homogenates were substantially reduced (P<0.01) by YE (at 0.5 mg ml ^-1), protease activity was increased (P<0.05), deaminase activity and activity against Ala ₂ were unaffected (P>0.05) and activity against Ala ₅ was reduced by 25% (P>0.05). When the homogenates from control and YE-supplemented (0.5 mg ml ^-1) vessels were used to inoculate roll tubes containing 0 or 5 mg ml ^-1 of YE, fewer colonies developed (P<0.01) in roll tubes containing YE than in those without YE, irrespective of the source of inoculum. Homogenates were also assayed for saponin degradation and for protease, peptidase and deaminase activities. Inoculum from the vessels receiving YE degraded saponin slightly during a 2 h incubation. Yucca extract at 0.5 mg ml ^-1 altered proteolytic activity and reduced protozoal numbers, but did not affect DMD or bacterial activity, and did not induce resistance to YE at a concentration of 5 mg ml ^-1.