Ruminal digestion of leguminous forage, potatoes and fodder beets in batch culture: I. Fermentation pattern

The effects on rumen fermentation of fodder beets and potatoes as substrates per se and as modifiers of the rumen microbiota were tested in two experiments using a 700 ml batch culture system. In the first experiment, seven diets were incubated for 5 h with rumen fluid from either dry cows fed at maintenance energy intake (MFL) or with rumen fluid from lactating cows adapted to fodder beets (BFL) or potatoes (PFL). Diets were: silage (S) or a mixture 60:40 on dry matter (DM) basis of silage and one of the following carbohydrate supplements: barley/oats 1:1 (BO), raw potatoes (RP), steam boiled potatoes (BP), frozen potatoes (FP), fodder beets (FB) or barley/oats/raw potatoes 1:1:2 (BORP). The silages were alfalfa (ASIL), grass (GSIL) and a mixture 1:1 (DM basis) of the two (AGSIL). Diets were ranked with respect to the amounts of carbohydrates fermented during 5 h as: FB=BP>BO>BORP>RP=FP=S, while rumen fluids in that respect were ranked PFL>BFL>MFL. FB diet did not result in butyrate proportions that differed from the BO diet. The rumen fluid means for butyrate proportion (mmol/mol total VFA, volatile fatty acids) were 80, 130 and 107 for MFL, BFL and PFL, respectively. The FB diet caused lactate concentrations of 72.3, 33.7 and 25.0 mmol/l for MFL, BFL and PFL, respectively. In the second experiment, a grass silage/barley diet (60:40 on DM basis) was incubated in the same in vitro system with rumen fluid from lactating cows adapted to 0, 1 or 2 kg DM potatoes. No linear trend for fermentation intensity versus potato inclusion was recorded, but rumen fluid from cows fed 1 kg DM potatoes had a shorter lag phase and slightly lower end-time pH (5.37 versus 5.48, P<0.001) than the two other rumen fluids. concluded that the larger amounts of substrate fermented with fodder beets or boiled potatoes have a potential to supply more energy for microbial synthesis than a barley/oat grain mixture or raw potatoes. Replacement of barley/oat grain by fodder beets should not imply any risk for decreased supply with glucogenic substrates as such a diet was found to maintain the propionate proportion of total VFA and besides produce substantial amounts of lactate, which would be converted to mainly propionate in vivo.