Twenty Chios newborn ewe lambs were used. Ten lambs were fed ad libitum colostrum and darn milk (group 1). The other ten lambs were separated from their dams immediately after birth and were not allowed to suckle normally, but were fed commercial cow's milk with a feeding bottle (group 2). When they were one year old, M. haemolytica serotype A1 (109 germs) was inoculated intratracheally to each ewe. Serum vitamin E and malondialdehyde (MDA) concentrations were determined in all the sheep before inoculation, and on days 1, 10, and 22 after inoculation, in addition to day 7 after antibiotic treatment. Serum vitamin E concentrations significantly decreased on day 1 after bacterial inoculation in group 1, rose on day 10 and continued to rise on day 22 after inoculation. The concentrations of the compounds did not significantly differ from the values observed on day 22 after antibiotic administration (on day 7 after treatment). Vitamin E concentration significantly decreased on day 1 after inoculation in group 2, and significantly rose on day 10 and then remained constant. Significant differences were observed between groups 1 and 2 before inoculation (P <= 0.05). While serum vitamin E concentration of group 1 was higher than group 2 before inoculation, the concentrations in group 2 were significantly higher than in group 1 on days 10 and 22 after inoculation. Serum MDA concentrations gradually significantly increased in groups 1 and 2 after bacterial inoculation (P <= 0.05), and then decreased to the pre-inoculation values after antibiotic treatment. No significant difference was observed between group 1 and group 2 on any sampling day. In conclusion, M. haemolytica infection induced lipid peroxidation associated with a rapid consumption of the antioxidant vitamin E (day 1), following by mobilisation of liver vitamin stores, probably more intense in ewes fed artificially after birth. The similar serum MDA concentrations in the two groups suggests that, a resistance against an infection can develop in sheep fed with artificially cow's milk within one year, but the effects of repeated infections on such animals still remains to be explored.