Autumn-cut grass silage as roughage component in dairy cow rations. 2. Rumen degradation, fermentation and kinetics

Abstract

In a 4 x 4 Latin square experiment the effects of DM content and/or the extent of fermentation in grass silages on the pattern of rumen fermentation and rumen kinetics were studied. In a separate study two cows were used to measure the rate of degradation using the dacron bag technique. Four rumen cannulated dairy cows were used to measure rumen fermentation pattern, rumen kinetics were measured in three of these animals. Basal diets (70% of total DM) consisted of maize silage, moist ensiled beet pulp, moist ensiled maize gluten feed, moist ensiled brewers' grains and a concentrate mixture. The remainder of the diet (30% of total DM) was wilted grass silage (WGS), high moisture grass silage with molasses (MGS), high moisture silage with formic acid (FGS) or wilted grass silage with additional water (WW). All diets were fed as complete feeds. pH of the rumen fluid was lower on the MGS and FGS diets. Concentrations of total VFA, acetic acid, ammonia and branched-chain fatty acids (BCFA) were highest on high moisture diets (MGS and FGS). Rates of clearance and digestion of the organic matter (OM) fractions were or showed tendencies towards being negatively influenced by both MGS and FGS, but remained unaffected by WGS and WW. Degradability of the grass silages was influenced by fermentation in the silo (lower digestible fractions and higher soluble fractions), as were rates of degradation (higher). Results of the degradability measured on the basal diet ingredients were in agreement with published literature and showed a strong correlation between OM digestibility in vitro and the undigestible fraction.