SREEDEVI, B (Major)SHOBHAMANI, BSREELATHA, ChVIJAYA SAILAJA, A2016-12-242016-12-242009-12http://krishikosh.egranth.ac.in/handle/1/92618ABSTRACT : Newcastle disease (ND) is one of the devastating poultry diseases which cause great economic loss to the rural poultry production. In the present study, the prevalence of the Newcastle disease antibodies in the rural poultry flocks was estimated by employing a single serum dilution Enzyme Linked Immuno Sorbent Assay (ELISA) kit. A total of 383 serum samples were collected from village chicken from different districts of Andhra Pradesh from both vaccinated and unvaccinated birds. The overall prevalence of ND in village flocks was found to be 77.81%. Out of 169 serum samples collected from vaccinated birds 91.72% were found to have antibody titres above protective levels. In the unvaccinated flocks, out of 214 samples 66.82% were found to have protective titres. Age wise analysis of the data showed maximum prevalence of the ND antibody levels in the 12-18 months age group. Sex wise analysis of the data revealed that there was no significant difference in the prevalence of ND in males and females. The present study indicated a higher prevalence of ND in the rural poultry flocks of Andhra Pradesh. The circulating strains of ND in the village chicken act as source of infection to the commercial poultry flocks. Vaccination is the only strategy for the control of the Newcastle disease in the poultry flocks. However, the presently available ND vaccines though they are effective in eliciting good immune response, they require maintenance of a cold chain from the point of production until they are delivered in the field which is very difficult under the village conditions. Hence, in the present study an attempt was made to develop thermostable mutants from the lentogenic ND vaccine strains. Lasota and F strains were cultured in the embryonated eggs and they were subjected to different heat treatments for thermostabilisation. Two different procedures were adopted for thermostabilisation, one is stepwise exposure to different temperatures for defined periods of time and the other is direct exposure to 56°C for different time intervals. In the stepwise procedure the Lasota and F strains were kept at 25°C, 37°C and finally at 56°C. Lasota strain could survive for 120 min after 11 successive cycles of heating whereas F strain could survive for 105 min after 11 successive cycles of heating at 56°C. Direct exposure of the strains to 56°C also yielded better results. The Lasota strain could withstand for 135 min after 19 successive heat treatments and F strain could withstand for 90 min after 16 successive thermal cycles. The mutants were found to have better thermostability than the parent viruses and they did not revert back to original even after back passages in the embryonated eggs. The stability of these mutant strains was checked by incubating the infectious allantoic fluids at 37°C for 35 days with and without addition of the stabilizers. The thermoresistant mutants were found to be more stable and addition of stabilizers improved the keeping quality of the strains. Further, these thermoresistant mutant strains were administered to experimental chicken to evaluate their immunogenicity. A control group of birds vaccinated with the parent strains were also maintained. The results of the experiment revealed that the heat treated mutants were also equally immunogenic as they produced similar Haemagglutination Inhibition (HI) titres as that of the parent vaccine strains. The infected allantoic fluids were titrated and checked for sterility. In the present study an attempt was made to develop thermostable mutants from the conventional lentogenic ND vaccine strains. These mutants were found to be highly stable and equally immunogenic in eliciting immune response to ND. As these vaccines can withstand high environmental temperatures, they can be used successfully under village conditions without 63 any need for cold chain facilities. However, a thermostable food pellet vaccine prepared from locally isolated strains of ND would be a better alternative for the control of the disease in village flocks.enNEWCASTLE DISEASE; poultry diseasesThesis