For the past years in Europe, the need for reliable alternative techniques to animal experimentation has been urged by ethical and legal prescriptions. In ruminant nutrition, dual outflow stirred-tank reactors (Hoover et al., 1976; Merry et al.,1987) have proved to be suitable for the accurate control of environmental conditions to study the metabolism of rumen microbes. Their ability to support a varied ciliate population, however, is uneven. As protozoa are major agents in the rumen microbial community, investigating the best set of general operating conditions to maintain their population at high levels is an important issue.
The study was conducted in six dual outflow continuous fermenters (working volume of 1.11) supplied with 30 g/day of a pelleted diet made of 750 g orchard-grass hay and 250 g ground barley per kg. The vessels were inoculated with the rumen contents from four wethers, each equipped with a rumen cannula and given a similar diet. They were continuously infused with an artificial saliva containing: Na2HPO4.12H2O 6.157 g/l, NaHCO3 5.268 g/l, KHCO3 0.597 g/l, NaCl 0.305 g/l, HC1-cysteine 0.4 g/l and alcalinized to pH 10.0 with 1.63 g/l NaOH. The fermentation broth was separately complemented with 31.7 mg CaCl2, 47.5 mg MgCl2 and 0.755 g (NH4)2SO4 per day.