الفهرس 
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Abstract
The efficacy of protection of prepared inactivated E. coli vaccines were compared with commercially available live attenuated E. coli (Paulvac®) vaccine. Four hundred and fifty one day- old broiler Cobb chickens were used. Gr (1) were kept as non vaccinated non challenged control negative gr, groups (2-5) were received monovalent prepared inactivated vaccine from E. coli O158 strain , O78 strain ,O114 strain , O125 strain ;respectively. While chicken gr (6) received inactivated prepared polyvalent vaccine contains O125,O44,O114,O158,O78 strains, gr (7) received both used polyvalent inactivated vaccine together with live attenuated E. coli vaccine, gr (8) received live attenuated E. coli vaccine only, finally gr (9) received both inactivated prepared O78 E. coli vaccine together with live attenuated E. coli vaccine. Groups (2-5) were challenged intra-crop with homologues viable serogroupsO158 strain , O78 strain ,O114 strain , O125 strain ; respectively. While grougs (6, 7, 8 and 9) were challenged intra-crop with heterologues viable serogroups O158, O78, O114, O125 and O44. Challenge was done 2 weeks after vaccination, followed by 10 days observation period, Performance parameters including body weight/ gm, feed intake and feed conversion rate (FCR) were calculated together with lesion score, clinical signs, mortality rate and histopathological findings were studied. Concerning results of final body weight in gram per each group by the end of the experiment result revealed that gr (7) showed highest average body weight in gram (1456.3 ± 87.5) followed by gr (9) which was (1425.0±154.1), then group (6) which was (1428.0±155.0), then gr (8) which was (1410.0±76.2) then control nonvaccinated group which was (1370±108.1) followed by group (5) which was (1344 ± 125.5) then group (2) which was (1305 ± 59.6) then group (3) which was (1288.7 ± 69.6) while group (4) was the lowest (1265.9 ± 76.6).
FCR results revealed thatgroup received live E. coli vaccine together with polyvalent inactivated E. coli vaccine (gr 7) showed best feed conversion rate (1.453) followed by both groups received live poulvac vaccine (group 8) and those received live poulvac vaccine together with inactivated O78 E. coli vaccine (group 9) which both showed same results (1.463) followed by group received polyvalent inactivated vaccine (gr 6) as it was (1.47) followed by group received inactivated O78 E. coli vaccine (gr 3) showed (1.485) then control negative group (group 1) which showed (1.497) feed conversion rate. Groups 2, 4, and 5 (inactivated O158 strain, inactivated O114 strain, inactivated O125 strain; respectively) showing the same results (FCR = 1.493).
No lesion score or PM lesions were detected in both vaccinated broiler chickens groups and control vaccinated non challenged group before challenge, while after challenge lowest lesion score were found in group received live commercial E. coli vaccine together with polyvalent inactivated E. coli vaccine.
Concerning mortality rate post challenge gr. 4 was the highest (22.2%), followed by groups 2 and 3 (16.8%) then gr 5 (11.1%) while other groups showing no mortalities. Histopathological findings revealed that, there were no characteristic changes observed in organs (trachea, lung, intestine and liver) of control negative non vaccinated non challenged groups. All vaccines did not cause any pathological changes post vaccination. After challenge groups received inactivated monovalent or polyvalent E. coli vaccine showed more sever histopathologicall changes than those received live Poulvac E. coli vaccine alone or combined with polyvalent or O78 strain.
It could be concluded that most of isolated E. coli isolates were pathogenic. Prepared monovalent and polyvalent inactivated vaccines were effective but the live attenuated commercial available E. coli (Paulvac®) vaccine had better protection.