Bioactive compounds, aucubin and acteoside, in plantain (Plantago lanceolata L.) and their effect on in vitro rumen fermentation

Plantain (Plantago lanceolata L.) contains bioactive compounds with antimicrobial activity that can potentially influence ruminal fermentation. This study aimed to identify the concentration of the bioactive compounds catalpol, aucubin, and acteoside in plantain cv. 'Ceres Tonic' through two consecutive growing seasons (2011-2012 and 2012-2013). Then the herbage with highest levels of bioactive compounds was used to evaluate their effect on rumen in vitro fermentation. Plantain cv. 'Ceres Tonic' had almost nil concentration of catalpol. Both aucubin and acteoside concentrations increased (P < 0.05) through the growing season. Aucubin increased from 1.78 to 3.80 mg/g DM in the first and from 0.44 to 6.87 mg/g DM in the second growing season; while, acteoside increased from 23.6 to 35.4 mg/g DM and from 0.5 to 41.7 mg/g DM, respectively. The in vitro experiment evaluated the effect of aucubin and acteoside on ammonia (NH3), volatile fatty acids (VFA) and gas production (GP) parameters. Aucubin and acteoside were added to chicory (Cichorium intybus L.) as negative and to plantain as positive controls. The treatments were (i) chicory (CH); (ii) chicory + 10 mg aucubin/g DM (C+au); (iii) chicory + 20 mg aucubin/g DM (C+2au); (iv) chicory + 40 mg acteoside/g DM (C+ac); (v) plantain naturally containing 7 mg/g DM of aucubin and 36 mg/g DM of acteoside (PL); (vi) plantain + extra 10 mg aucubin/g DM (P+au); and (vii) plantain + extra 36 mg acteoside/g DM (P+ac). Plantain with natural concentrations of bioactives produced 40% less NH3 than chicory over 24 h. The exogenous addition of both bioactive compounds reduced net NH3 production by CH and PL. The increase in potential GP from acteoside fermentation suggested its use as an energy source. Whereas, the addition of aucubin reduced the rate of GP at dose level, potentially due to its bactericide activity. Therefore, acteoside would have a greater positive effect than aucubin on ruminant animals.