The purpose of this study was to determine the relationship between tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) cytokines and experimental Mannheimia haemolytica (M. haemolytica) infection in ewes that had been fed colostrum and dam milk or commercial cow milk after birth. Twenty one-year-old Chios ewes were fed colostrum and dam milk (n=10) or commercial cow milk (n=10) after birth while they were lambs. Feed and water were given ad libitum. Ewes were inoculated intratracheally with I x 10(9)M. haemolytica Type A1 in 2 ml of PBS. Blood samples were collected from the jugular vein once before bacterial inoculation and 3 times at day 1, 10 and 22 after bacterial inoculation from all animals. Antibiotic treatment was applied at the 22th day. Blood samples were also collected at day 7 of the treatment. Serum samples were stored in -70 degrees C until analysed. Serum TNF-alpha, IL-1 beta and IL-6 levels were assayed by enzvme-linked immunosorbent assay. Test results were analysed using a Student's t test between two groups an one way ANONA between blood sampling days. The levels of TNF-alpha, IL-1 beta and IL-6 in ewes fed colostrum and dam milk tended to be higher than in ewes fed commercial cow milk; the differences, however, were not statistically significant. All levels insignificantly increased after bacterial inoculation and then gradually decreased. The results may indicate that the inflammatory response of ewes fed colostrum and dam milk after birth is relatively more potent than of ewes fed artificially. However, the differences observed in this study were not statistically significant.