High methanogenic potential of sucrose compared with starch at high ruminal pH

The role of ruminal pH with respect to the expression of a differentiation in the methanogenic potential of easily fermentable carbohydrates was determined using the rumen simulation technique. The target pH at 21 h after feed supply was set to 6.0 and 7.0 through a specific buffer management. A basal diet was supplemented with crystalline sucrose or steamflaked maize starch. With sucrose instead of starch, the decline in fermenter fluid pH, 4 h after introducing new feed, was more pronounced at both buffer levels, and degradability of all nutrients, including fibre was higher too. At low pH, molar propionate proportion was higher with sucrose. Methane quantity depended on the combination of pH and source of easily fermentable carbohydrate as sucrose, compared with starch, enhanced methanogenesis (+40%), but only at the high pH. The concomitant increase in organic matter degradability with sucrose at high target pH did not completely explain this phenomenon, as the effects on methane were still significant when related to apparently fermented organic matter. However, differences caused by pH and carbohydrate type decreased when methane was related to degraded fibre, suggesting that there was a mutual supportive effect of high pH and sucrose on fibre degradation.