The main objective of this study was to determine the effects of different silage additives on protozoan population, genera and total volatile fatty acid (VFA) concentrations and percentage of VFAs in corn silage. Four ruminally fistulated Morkaraman x Kivircik lambs were used in a 4 x 4 Latin square design with 14-day adaptation and 1-day sampling periods. The animals were offered 20% cottonseed meal and 80% corn silage with or without treatment with silage additives, ad libitum intake. Silages used in the experiment were corn silage without treatment, treated with 5% molasses, 0.05% formic acid, and 10 g/t enzyme. Total protozoan number was significantly different among treatments (P < 0.05). It was the highest in sheep fed silage treated with molasses (313.2 × 103 ml-1) and the lowest in sheep fed silage treated with formic acid (168.0 × 103 ml-1). Entodinium, Epidinium, Isotricha, Dasytricha, Diplodinium, and Osphyroxscolex types were observed in all treatments, but major protozoan genera were Entodinium, comprising 61-69% of total protozoan population. Total VFA concentration was significantly less in sheep fed enzyme-treated silage compared with other treatments. Percentage of acetic acid was significantly lower (P < 0.05) in sheep fed silage treated with molasses compared with other treatments, but percentages of propionic acid, and butyric acid were similar among treatments. Ruminal ammonia-N concentrations ranged from 7.71 to 15.87 mg/dl and were lowest in sheep fed enzyme-treated silage among treatments (P < 0.05). In conclusion, the highest protozoan counts were observed in the rumen of sheep fed corn silage treated with molasses. © 2003 Elsevier Science B.V. All rights reserved.