Influence of cultures of Aspergillus oryzae on rumen and total tract digestibility of dietary components.

Three trials were conducted to evaluate the effect of dried cultures of Aspergillus oryzae on nutrient utilization by mature Holstein cows fitted with ruminal and duodenal cannulas. In trial 1, four cows (two dry and two lactating) were used to test Aspergillus oryzae (3 g/d) and a control treatment at two forage amounts in a 4 x 4 Latin square. Trial 2 compared control, A. oryzae, and Saccharomyces cerevesiae using six lactating cows in a repeated 3 x 3 Latin square design. For trial 3, four lactating cows were used in a switchback design to compare control to A. oryzae treatment. In trials 2 and 3, diets contained 70 and 61% concentrate. A fourth in vitro trial was conducted in conjunction with trial 3 in which rumen fluid was obtained from cows adapted or unadapted to A. oryzae. On all trials except high forage in trial 1, A. oryzae increased rumen and total tract digestibility of fiber fractions. Rumen VFA and ammonia were not affected by fungal cultures. Aspergillus oryzae increased rate of rumen fermentation of alfalfa but not of milo or wheat straw. In vitro disappearance of DM from alfalfa, milo, and wheat straw was increased by A. oryzae, and previous adaptation was not required to stimulate in vitro DM digestibility. These results indicate that a primary effect of A. oryzae is stimulation of fiber digestion by rumen microbes.