Effect of buffer pH on methane production and fermentation characteristics of three forages tested in vitro

Low rumen pH is proposed to be a major mechanism for low methane (CH₄) emissions from sheep fed forage rape. However, it is difficult to separate this from other in vivo factors, such as rumen passage rate. The objective of this study was to determine the effect of pH alone on CH₄ production in vitro using different pH buffers. Ryegrass, white clover and forage rape were incubated in vitro using three different incubation buffers with starting pH values of 5.5, 6.2 and 6.8.

Decreasing pH reduced overall in vitro CH₄ emission relative to fermented hexoses (CH₄/FHex) by up to 54% and overall fermentation by 40%. pH also changed fermentation profiles where the acetate + butyrate to propionate + valerate ratio decreased when pH decreased. Within the three forages, forage rape led to the lowest CH₄/FHex, but only in pH 5.5 and 6.2 buffer, and this was enhanced when the pH fell below 6.

Reducing pH in vitro decreased CH₄ production and overall fermentation across all forages. The lower pH reached by forage rape compared to ryegrass and white clover appears to drive the lower CH₄ production relative to the extent of fermentation from forage rape compared to the other forages. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.