BG-IV GENE EXPRESSION AND ITS ASSOCIATION WITH IMMUNE RESPONSE TRAITS IN NIGERIAN LOCALLY-ADAPTED TURKEYS CHALLENGED WITH ATTENUATED ANTIGENS OF NEWCASTLE DISEASE VIRUS
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2024-09-20
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A thesis submitted to the Department of Animal Breeding and Genetics, College of Animal Science and Livestock Production, Federal University of Agriculture, Abeokuta in partial fulfillment of the requirement for the award of degree of Doctor of Philosophy in Animal BiotechnologyABSTRACT
Newcastle Disease (ND) is a significant challenge in poultry production, severely affecting the sector's profitability. Prophylactic vaccination and disease prevention strategies have proven insufficient in managing outbreaks and minimizing losses. Integrating genetic resistance mechanisms are crucial for effective disease management. The BG-IV gene, unique to avian species like turkeys, play a vital role in mounting immune responses during pathogenic challenges. This study examined the expression of the BG-IV gene and its correlation with certain immune response characteristics in Nigerian locally adapted turkeys (NLAT) exposed to Newcastle Disease Virus (NDV) attenuated antigens. 201 F1 generation turkey poults were used for the study. At three weeks of age, the poults were challenged with 1% Sheep Red Blood Cell (SRBC) solution in order to classify the antibody titre. Both innate (cytolytic) and adaptive (latent) immune response traits were assessed. BG-IV gene expression at these stages was determined by inoculating the poults with attenuated NDV (Type B1 Lasota) vaccine at 5 weeks of age. Blood samples and tissues from immune organs (thymus, spleen, and liver) were collected 5 and 7 days post-inoculation from an equal number of high titre and low titre poults, considering sex and plumage colour. Blood samples were subjected to haematological and serum biochemical analyses. mRNA from immune tissues was extracted and quantified using quantitative polymerase chain reaction (qPCR) to determine the relative expression of the gene at both phases. The mean expression levels of the BG-IV gene in the tissues at different response phases were computed using the double delta Ct analysis method. The association between immune response traits and BG-IV gene expression was determined using correlation and step-wise regression analysis in SAS software. The haematological profile of NLATs at 5 days post-inoculation was not significantly (P≥0.05) affected by sex, titre class, or plumage colour. White plumage-coloured turkeys exhibited the best aspartate transaminase, Alanine Amino Transferase, and alkaline phosphatase values at 5 dayspost-inoculation, while turkeys in the high titre class had the best RBC, WBC, and basophil values at 7 days post-inoculation. The BG-IV gene was expressed in all examined immune organs in response to immunological challenges by attenuated antigens of the ND virus at both the cytolytic and latent stages. Low correlation coefficients were observed between BG-IV gene expression and the haematological profile of NLATs at 5 and 7 days post-inoculation. Neutrophil and Alanine Aminotransferase were associated with BG-IV gene expression at the cytolytic stage of the immune response, while basophil was associated with BG-IV gene expression at the latent stage. Neutrophil and Alanine Aminotransferase can serve as predictors for BG-IV gene expression at the cytolytic stage, while basophil can be used as a predictor at the latent stage in NLATs. The BG-IV gene can be utilized as a marker for innate immunity and treatment responsiveness in turkeys. It is recommended that male NLATs with white plumage colour, belonging to high titre class be used for improving immune traits and immune responsiveness to pathogenic challenge.