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The thesis is divided into two parts namely, studies A and B. The objective of study A was to conduct a phylogenetic analysis on the predominant v-NDV strain in Lebanon, to develop an autogenous Newcastle Disease Virus (NDV) vaccine aiming at the control of v-NDV, and to evaluate its degree of protection and immunity in Eimeria-infected birds. A blend of eucalyptus and peppermint essential oils was also incorporated in this study to explore if essential oils have any immunopotentiating effect when administered to birds subjected to v-NDV and Eimeria challenges. A controlled challenge trial was conducted. Eighty day-old chicks were divided evenly into 8 different experimental treatments. Treatments 1, 2 and 3 were vaccinated with the developed NDV vaccine at d1 and d14, and received Eimeria challenge at d21 and v-NDV challenge at d28. The positive control Treatments 4 and 5 did not receive any NDV vaccination, and received both challenges. Treatments 6, 7, and 8 received the developed NDV vaccine, however they did not receive any challenge, acting as negative control for NDV. Evaluation of protection included an assessment of performance parameters namely, the percent weight gain, feed conversion, mortality, and specific acquired immunity to the hemagglutinin and fusion proteins of the v-NDV. The priming and boosting with the developed autogenous vaccine conferred a 100 percent survival in Eimeria-infected and uninfected birds that were challenged with v-NDV compared to 0.0percent and 30.0percent survivals in unvaccinated-challenged controls (P0.05). The acquired HI titers to hemagglutinin and fusion proteins of …