Haileleul NegussieKuastros Mekonnen2026-08-072026-08-072012-06-01https://etd.aau.edu.et/handle/123456789/8815This experimental study was undertaken from December 2011 to May 2012 with the objective of determining the efficacy of adjuvated formalin killed experimental Mannheimia haemolylica vaccine prepared in this study from serotypes of this organism: serotype A2, A7 and combined serotypes (A2 and A7) for ovine pneumonic pasteurellosis. The efficacy was determined by using indirect haemagglutination (IHA) titer and challenge protection test. This experiment used 47 clinically healthy male lambs and grouped in to four treatment groups, group 1 with 14 lambs receive A2 serotype vaccine, group 2 consists of 13 lambs and vaccinated by serotype A7, the combined serotype vaccinated and the control are group 3 and 4, respectively and each consist of 11 and 9 lambs, respectively. Pre vaccination titer was measured from all lambs to assess their exposure and found that all lambs showed a moderate titer. This experimental vaccine was injected subcutaneously with a single dose to the vaccinated groups. All the vaccinated groups showed a significant higher IHA log10 titer at the 3rd and 4th week post vaccination than the controls. At the 3rd week a relative higher titer was observed in A 7 and the combined serotype vaccinated groups having a GM antibody titer of log 1 01.65 and log 10 1.66, respectively. Similarly, at 4th week a higher titer was observed in A7 and combined serotype vaccinated groups having GM titer of log 101.58 and log 101.57, respectively. There was no significant difference in serotype A2 vaccinated groups at the 3rd and 4th week of post vaccination than A7 and the combined serotype vaccinated, but the IHA test result revealed lowered GM titer (log10 1.60 and log101.45) for the respective weeks. Post challenge clinical investigation showed that significant higher morbidity was seen in control group expressed by 1.50C increase in rectal temperature and respiratory signs. Following intra tracheal challenge only 3 (15%) lambs from vaccinated group were found to have a + 11ung lesion score. 100% of the lambs in unvaccinated control group were found to have lung lesion scores between +2 and +3 , but no significance difference between the different vaccinated groups. This experiment also found a moderately weak correlation (r2=0.314) between antibody titer and extent of lung lesion score. Therefore, the tested experimental vaccines showed sufficient efficacy especially A7 and the combined serotypesenMannheimia haemolylicalambschallenge protectionindirect haemagglutinationThesis