Forage Level and Methane Inhibitor Effects on In Vitro Fermentation Products Using Forage Rape or Ryegrass as Substrates

Dietary approaches that decrease ruminal pH may be combined with anti‐methanogenic feed additives that prevent methane formation and consequently increase the dissolved hydrogen concentration. To evaluate the effect of pH and the effect of dissolved hydrogen concentration, two forages (forage rape and ryegrass) were incubated in vitro at two forage levels (FL 1% and 2% w/v) with or without bromoform (3 µM). The combination of bromoform and FL 2% did not affect gas production or fermented hexose equivalents compared to both factors tested separately. The ratio of acetate‐to‐reduced products decreased greatly by combining FL 2% and bromoform (0.59 mmol.g −1 /mmol.g −1 ) compared to FL 1% and bromoform (0.79 mmol.g −1 /mmol.g −1 ). The production of reduced products increased by a similar proportion to the decrease in acetate. Ryegrass fermentation decreased by 8% with bromoform addition, while the forage rape fermentation was not impaired, even though the hydrogen released from forage rape (43.5 ml/g) was twice that released from ryegrass (21.5 ml/g). Results suggest that the combination of low pH and high hydrogen (achieved by 2% FL and bromoform addition) did not cause detrimental effects on feed fermentation in vitro, but ryegrass fermentation may be impacted by high dissolved hydrogen.