الفهرس 
Introduction
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Abstract
This study was designed to evaluate the protection efficacy of some different vaccination IBD programs in commercial broilers, which had a high IBD MDAbs level to mimic the field conditions and to overcome the IBD challenge.
A total Number of 350 one-day-old Ross broiler chicks reared for 42 days in a clean well-ventilated floor pens and divided into seven groups of chicks 50 birds
each.
group A was vaccinated by using 0.1 ml Vector vaccine (HVT+ IBD) at 1 day old via S/C injection at the hatchery. group B was vaccinated by using
0.1ml live immune complex vaccine at 1 day old via S/C injection at the hatchery. group C was vaccinated by using live intermediate plus vaccine at 14th day via eye drops. group D was vaccinated by using both live intermediate vaccine at 7th day plus live intermediate plus vaccine at 14th day via eye drops. group E was vaccinated by using live intermediate vaccine at 12th and 22th day via eye drops. group F was vaccinated by using both Vector vaccine (HVT+ IBD) at 1 day old via S/C injection at the hatchery plus live intermediate vaccine at 12th day via eye drops. group G considered the control group (did not receive any I.B.D vaccination).
Blood samples were collected at day one old chicks to detect the maternal antibody level. Blood and bursa samples were collected at 7 (7dpv), 14, 21, 28, 35 and 42 days (7 dpch) days from groups A, B and G and collected at 14 (7dpv),
21, 28, 35 and 42 days from group D and at 21 (7dpv), 28,35 and 42 days from groups C, E and F. All the experimented groups were challenged at 35 days with virus suspension of vvIBD field strain.
The efficacy of HVT-IBD vector, immune-complex, and live IBD vaccines, either intermediate or intermediate plus, were compared through differentvaccination programs to evaluate their efficacy; the following parameters have been estimated including bursa body weight ratio (BBR), bursa score index (BSI), ELISA IBD antibody titer, Serum nitric oxide concentration (serum NO) and histopathological examination of the bursa.
The highest BBR and BSI were observed in the group vaccinated with HVT-
IBD at hatchery) which was close to the control group followed by the group vaccinated with HVT-IBD at hatchery plus live intermediate vaccine at 12th days. While the other groups showed a reduction in the BBR and BSI which became significant between the group vaccinated by using live intermediate vaccine at 7th day and live intermediate plus vaccine at 14th day and control group.
The group vaccinated with double doses of live intermediate vaccine
(Intermediate Lukert strain) at 12th and 22th days had a higher BBR than the group vaccinated with immune complex vaccine at hatchery and the group vaccinated with live intermediate plus vaccine at 14th day.
The vvIBDV challenge resulted in decreased BBR and BSI at 42 days (7dpch)
in all the vaccinated groups and in control positive group (non vaccinated challenged). Which became significant between these groups and the control negative group (non vaccinated, non challenged).The bursal index results showed that the bursa were atrophied in all vaccinated groups post challenge with indices below 0.7 which indicated that none of these vaccines could prevent damage of the bursa of Fabricius
Broiler chicks in this study hatched with high MDAbs (5645.18±346.62)
which declined to reach 366.60±29.03 in the non-vaccinated control group at 21 days of age.
The group vaccinated with HVT-IBD vaccine at hatchery and the group vaccinated with HVT-IBD and live intermediate vaccine at 12 days the antibody titers using IDEXX IBD ELISA was negative. Therefore the HVT-IBD groups retested using ProFLOK® IBD PLUS ELISA that allows the detection of VP2 antibodies, which specifically induced by the HVT-IBD vaccine. And the results showed a positive Seroconversion following vaccination which begins at 21 days (three weeks post vaccination) confirming that HVT-IBD vaccine efficacy is not affected by the presence of high levels of MDAbs. The ELISA antibody titers increased markedly at, 28 and 35 days but there was no significant difference in antibody titers between these two groups.
Following vaccination with the immune complex vaccine a positive IBD ELISA titer detected at 21 days and the titer shows a noticeable increase at 28 and
35 days.
The group vaccinated with intermediate plus strain of I.B.D.V (IBDV strain W2512) at 14 days of age the ELISA antibody titer considered negative at 7 days post vaccination (at 21 days) but the seroconversion was positive after 14 days vaccination (at 28 days) and showed a marked increase at 21 days post vaccination (35days).
The group vaccinated by live intermediate vaccine at 7th days of age (Intermediate Lukert strain) and live intermediate plus vaccine (IBDV strain W2512) at 14th day of age gave a positive ELISA antibody titers starting from 21 days.
Two doses of intermediate live vaccine (Intermediate Lukert strain) at 12 &
22 days resulted in negative IBD ELISA titer at 21 and 28 days however, at 35 days a positive seroconversion was detected.
ELISA results explicate an immunity gap in group vaccinated with intermediate plus strain of I.B.D.V till 28 days of age and also in group vaccinated with two doses of intermediate live vaccine at 12& 22 days till 35 days.
After Challenge of chickens with vvIBDV a seroconversion was detected which was reflected by higher ELISA antibody titer in the challenged groups than in the non-challenged one. The highest antibody titer was detected in the group vaccinated by two doses of intermediate live vaccine (Intermediate Lukert strain) at
12 & 22 days and the lowest antibody titer was detected in group vaccinated by
HVT-IBD at hatchery followed by live intermediate vaccine at 12 days.
Vaccines raise a low level of NO leading to increase in macrophage production witch increased gradually to reach its highest concentrations at 35 days (before challenge). And reach it maximum peak at 42 days (7dpch) that may promote cellular destruction and bursal necrosis. group D, which had the highest NO concentration after challenge, had also the highest bursal lesions and oppositely group A which had the lowest NO concentration after challenge had the lowest bursal lesions.
In this experiment, the distribution of the observed histopathological lesions is variable within the different ages post vaccination and after challenge. The non- vaccinated control group did not show any histopathological lesion at 7, 14 and 21 days. However, at 35 days, the bursa started to show a regression of some of the bursal follicles and at 42 days (7dpch) the non-vaccinated not challenged groups showed mild exhaustion and depletion of lymphocytes in lymphoid follicles while the challenged control broiler chicken showed very sever exhaustion and depletion of lymphocytes, follicular necrosis, vacuolation in follicular area and fibrosis in the interfollicular connective tissue.
The group vaccinated with HVT-IBD at hatchery followed by the group vaccinated by HVT-IBD at hatchery and live intermediate vaccine at 12th days had the lowest histopathological lesions of bursa. No adverse pathological lesion detected in the bursa in-group a at 7, 14, 21 and 28 days of age of the bursa is similar to the control group. However, at 42 days (7dpch) there is a mild exhaustion and depletion of lymphocytes in lymphoid follicles of the bursa.
group vaccinated with immune complex vaccine at hatchery displayed normal histological results close to the control group at 7 and 14 days. The histopathological lesions in bursa of Fabricius was firstly demonstrated at 21 days with mild exhaustion and depletion of lymphocytes which increased at 28 days to show moderate exhaustion and depletion of lymphocytes and at 35 days there is a moderate to severe exhaustion and depletion of lymphocytes in lymphoid follicles and increased interfollicular connective tissue. After challenge, the bursa showed severe exhaustion and depletion of lymphocytes in lymphoid follicles, necrosis, follicular vacuolation, increased interfollicular connective tissue and multiple intrafollicular cysts.
group vaccinated with intermediate plus vaccine (IBDV strain W2512) at
14th day of age. The histopathological examination of the bursa at 21 days showed mild to moderate exhaustion and depletion of lymphocytes in lymphoid follicles at
28 days there is epithelial necrosis, moderate to severe exhaustion and depletion of lymphocytes and intrafollicular cyst while at 35 days bursa was atrophied with moderate exhaustion and depletion of lymphocytes, increased interfollicular connective tissue and intrafollicular cyst. After challenge at 42 days, very sever exhaustion and depletion of lymphocytes in lymphoid follicles, necrosis and vacuolation in follicular area, and increased interfollicular connective tissue.
In the group vaccinated by live intermediate vaccine at 7th days of age
(Intermediate Lukert strain) and live intermediate plus vaccine (IBDV strain W2512)
at 14th day of age examination of bursa of fabricius showed the worst histopathological results started at 21 days with moderate to severe exhaustion and depletion of lymphocytes progressed at 28 days to show follicular necrosis with cystic formation, sever exhaustion and depletion of lymphocytes and at 35 days exhibited atrophied bursa with moderate to severe exhaustion and depletion of lymphocytes and increased interfollicular connective tissue. At 7dpch the bursa displayed a very sever exhaustion and depletion of lymphocytes in lymphoid follicles, necrosis and vacuolation in follicular area, and increased interfollicular connective tissue.
Double dose vaccination with live intermediate vaccine (Intermediate Lukert strain) at 12th and 22th day) showed histopathological results in bursa which appeared as mild exhaustion and depletion of lymphocytes in lymphoid follicles at 21, 28 and
35 days of age. After challenge, the bursa showed moderate exhaustion and depletion of lymphocytes in lymphoid follicles, increased interfollicular connective tissue and multiple intraepithelial cyst.