Three Polish Merino sheep fed hay and ground barley were defaunated and then refaunated consecutively with only one (Eudiplodinium maggii), two (Eudiplodinium maggii and Entodinium caudatum) or three (Eudiplodinium maggii, Entodinium caudatum and Dasytricha ruminantium) ciliate species. Both the concentration and production rate of total VFA as well as the proportion of individual acids were estimated before the morning feeding and 4 h thereafter. The concentration of VFA varied from 8.2 to 11.6 mM/100 ml of rumen fluid and production rate from 29.1 to 34.1 µM/g rumen digesta/h in relation to the time after feeding. Molar proportion of acetate, propionate and butyrate in the total VFA in the rumen or produced in vitro was 65.1–74.6, 16.0–21.2 and 9.1–11.8 %, respectively. The concentration of VFA as well as production rate and molar proportion of individual acids were influenced by ciliates and composition of the fauna. Presence of Eudiplodinium maggii in the rumen resulted in the highest proportion of butyrate at 4 h after feeding. Establishment of ciliates in the rumen of sheep was accompanied by the drop in acetate proportions. No effect of ciliates on pH values before feeding was found whereas increase in the acidity of rumen fluid after feeding was affected by the fauna composition.