الفهرس 
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Abstract
This work aimed to throw light on the pathological changes after vaccination for certain diseases in poultry (Newcastle, infectious bronchitis, infectious bursal disease) and study cross vaccinations and their effect on lymphoid organs of boilers .
Samples of one –day-old broiler’s chicks (Habbard) obtained from two farm in El-Menofia governorate were investigated for evaluation of the field vaccination programs, for histolopathological studies. Three chicks were taken randomly from each farm at different intervals (one day pre-vacination, one day P.V., 5 day P.V., 10 day P.V., 15 day P.V.). The lymphoid organs (bursa of fabricius, thymus, spleen , cecal tonsils, HG and bone marrow) were collected from chicken and immediately fixed in 10% neutral buffered formalin solution.
Clinical signs were in the form of depression and diarrhea at all post vaccination. Grossly some chickens at farm I had Spleenomegaly and atrophy of bursa at P.V. of (Gumboro), while post vaccination of (Newcastle, Gumboro) all chickens was spleenomegaly and bursa enlarged.
Microscopically lesions of farm I P.V. of (Newcastle, IB) by D.W. at 8 days old, in the form of mild changes from congestion or hemorrhage or oedema and few heterophils in bursa but in thymus was depletion of lymphocyte. While the bone marrow showed activation of fat cells then activation of erythropiotic cells at 5 day post vaccination, then P.V. of (Gumboro) by D.W. at 14 days old, showed bursa at 5 day P.V. congestion of blood vessels, depletion of lymphocytes, few of heterophils, hyperplasia in epithelium, with marked cystic formation.
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Thymus and spleen revealed congestion, hemorrhage and depletion of lymphocyte. Cecal tonsils showed mild to moderate lymphocytic proliferation. HG showed moderate inflammatory cells infiltration and pronounced degeneration of the acini. Bone marrow showed decrease number of fat cells, proliferation of erythropiotic cells, and recognized proliferation of granulocyte cells.
Post vaccination by (Newcastle, Gumboro) with D.W. at 23 days old, showed increased severity of lesions in bursa, thymus and spleen. In addition to proliferation interfollicular connective tissue, completed loss of medulla and cortical cellular structure and marked papillary formation in bursa. Also thymus showed sever degeneration and sever depletion of lymphocytes in most of splenic tissue with fibrosis. While cecal tonsils showed massive proliferation of lymphocyte. HG showed degeneration and atrophy of acini, massive proliferation of lymphocyte cells. Bone marrow increase number of granulocyte and decrease number of erythropiotic cells but at 5 day P.V. increase fat cells in number and size till at 15 day P.V. the majority of cellular part of tissue replaced with fatty cell and residue of hemopiotic tissue then activation of erythrocyte.
Microscopically lesions of farm II P.V. of (Newcastle, IB) by D.W. at 8 days old, showed mild changes in bursa, thymus and spleen, while cecal tonsils showed mild proliferation to lymphocyte. Some cases of HG showed mild proliferation of inflammatory cell. Bone marrow proliferation to granulocytic cells and moderate absence to fat cells. Then P.V. of (Influanza, Newcastle) S.C. at 14 days old. Bursa showed depletion of lymphocyte, recognized epithelial hyperplasia and cystic formation. Thymus showed hemorrhage, congestion and vacuolization. Spleen showed oedema and small focal hemorrhage. HG showed moderate proliferation of inflammatory cells, atrophy of acini and marked
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cystic formation. While cecal tonsils and Bone marrow showed no variation.
Post vaccination of (Gumboro) with D.W. at 15 days of age. Bursa, thymus and spleen showed marked lymphocytic degeneration, with heterophils, moderate cystic formation and fibrous tissue proliferation in bursa . Thymus showed activation to Hassall’s corpuscles. While cecal tonsils, HG and bone marrow showed increased proliferation of lymphocyte and inflammatory cells, in addition to degeneration of acini, fibrosis formation and cystic formation in HG. Bone marrow showed proliferation of granulocytes and erythropiotic cells with few fat cells.
Post vaccination of (Newcastle, IB) with D.W. at 20 days of age, showed bursa, thymus, spleen had sever lymphocytic degeneration, sever hemorrhage, congestion and sever cystic formation. Also bursa showed connective tissue proliferation and heterophils cells. Spleen showed depletion of lymphocytes. While cecal tonsils and HG showed moderate to sever proliferation of inflammatory cells and lymphocyte with moderate hemorrhage in addition to degeneration of acinar epithelium with massive cystic formation in HG. Bone marrow showed focal aggregation of small lymphocytes with few number of reticuloendothelial then localized hemorrhagic areas distributed between hemopiotic tissue at 15 day post vaccination .