Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 5 4 2013 12 15 418 421 EN Razieh Talebzadeh Department of Animal Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran. Daryoush Alipour Department of Animal Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran. 2015 10 16 Background and Objectives: Essential oils may improve the utilization of nutrients by ruminal microorganisms. The aim of this study was to assess the effect of different doses of ajowan essential oils (AEO) on growth and fibrolytic activity of anaerobic fungi, and generic distribution of ciliated protozoa (in vitro). Material and Methods: Different doses of AEO (0, 150, 300, 450 and 600 ppm) were added to experimental tubes. The effect of AEO was evaluated on growth and fibrolytic enzyme activity of an anaerobic fungus (Neocalimastix spp.). Generic distribution of ciliated protozoa were evaluated in response to different doses of AEO. Results and Conclusion: The growth of fungus (Neocalimastix spp.) were inhibited and activity of fibrolytic enzymes of fungus were reduced by adding AEO. Also, an inhibitory effect was seen in concentration of ciliated protozoa and some genus were completely disappeared at the doses of 300 ppm and higher. The doses used in this study reduced the fibrolytic activity of the studied rumen microorganisms which is undesirable in practical animal nutrition. Further research is needed to assess the effects of AEO at lower doses on these parameters and also proteolysis and methanogenesis. https://ijm.tums.ac.ir/index.php/ijm/article/view/484 https://ijm.tums.ac.ir/index.php/ijm/article/download/484/260