Probiotics (microbial preparations and their growth media) are of increasing interest as feed additives for both ruminant and non-ruminant livestock. Amaferm is a fermentation extract prepared from cultures of the fungus Aspergillus oryzae which, when included in the diet of dairy cows, increases the yield of milk and buttermilk (Harris et al. , 1983). These improvements have been associated with changes in rumen fermentation (Weidmeier et al., 1987). The present study describes the use of the rumen simulation technique Rusitec (Czerkawski and Breckenridge, 1977) to investigate the effects of increasing doses of Amaferm on the stoichiometry of rumen fermentation in vitro.

Amaferm was added at 0, 25 and 250 mg/d to duplicate Rusitec vessels and at 1 g/d to a single vessel, receiving 10 g/d of a mixed diet of hay, barley, molasses, fishmeal and vitamins/minerals (500, 299-5, 100, 91 and 9.5 g/kg DM respectively). Vessels were initially inoculated from animals receiving the same diet. Artificial saliva was continuously infused into the vessels (total volume 850 ml, dilution rate 0.88/d) and feed bags were changed daily such that each bag was incubated for 48 h. Samples were taken at the time of feeding after 15 d adaptation to Amaferm.

Amaferm had no influence on total VFA concentrations but there was a shift towards an increased proportion of butyrate as the level of addition increased. Ammonia production was also stimulated by the addition of Amaferm, with the concentration in the vessel receiving 1 g/d being almost twice that found in the control vessels. There was no effect on dry matter disappearance after 48 h. The concentration of methane in the gas collected from the head space of the vessels was decreased by Amaferm, with the maximum decrease (17%) being seen at the level of 250 mg/d.