| Newcastle disease is one of acute, febrile and highly contagious diseases, which is caused by Newcastle disease virus. This disease causes tremendous economic losses to poultry industry in China every year. With the extensive application of the vaccines and the change of the concept of animal production, Newcastle disease has been controlled obviously. Among them, the immunization program plays a crucial role in this progress. Due to differences between the prevalence of disease and management, breeding levels and vaccine types in different areas, immunization procedures are also different. Especially in recent years, vaccinated chickens suffer from disease frequently in China, which is caused by many factors, such as different levels in safe requirements of poultry breeding, diversified breeding ways, different immune procedures and immune inhibition. During 2010 to 2011, I conducted point-fixed survey at a layer farm in Shanxi province. By setting several immunity test groups and measuring serum antibodies, the effects and the factors for immune efficacy were systematically studied in order to provide reliable evidence for formulating immune procedure of Newcastle disease. The results are as follows:1. The day-old chickens were measured for their maternal HI antibodies of Newcastle disease virus in different ages. The results showed: The maternal HI antibody in 1 day-old chickens was 6.6 log2, and in 7 day-old was 4.7 log2; The maternal HI antibodies droped to less then 4 log2 in 10 day-old age. When the threshold of antibody titer is 4 log2, the protection rate of maternal antibody was 95% for 1 day-old chickens, the protection rate was 80% for 7 day-old chickens, and the protection rate of maternal antibody was only 50% for 10 days-old chickens.2. Forty-two chickens were divided into three groups randomly, and the level of maternal antibodies were detected on 7 days-old chickens. At the same time, the chickens were vaccinated with attenuated Newcastle disease vaccines. The HI antibodies were detected on 17 day-old and 25 day-old chickens. The results showed: Maternal antibody titer(4.2 log2) increased by 0.2 titer at 17 days-old, and increased at titer of 5.9 log2 at 25 day-old; Maternal antibodies titer(3.6 log2) increased by 0.5 titer at 17 days-old, and increased at titer of 5.2 log2 at 25 day-old. However, maternal antibody titer(4.7 log2) decreased by 0.4 titer at 17 days-old, and only increased at titer of 4.8 log2 in 25 day-old chickens.3. Three groups of chickens were vaccinated with attenuated vaccines of Newcastle disease on 7 day-old, with three different immune procedures. HI antibodies were detected on 10 day-old and 18 day-old. The results showed: The antibody titers rose fast, which vaccinated with inactivated vaccines of Newcastle disease on 10 days-old and vaccinated with attenuated vaccines of infectious bursal disease on 12 day-old at the same time.4. The antibody levels of Newcastle disease vaccine were checked every month. Test results showed that antibody levels in chickens decreased at the first, and then rose. The chickens had a good protection because higher antibody levels. Layers had a strong immunity against Newcastle disease virus when antibody levels were between 8 log 2 to 10 log 2.5. To monitoring Newcastle disease antibodies in chickens from time to time, HI antibody levels in young chickens were low ( the antibody titers between 5 log2 to 7 log2), the qualified rate of antibody was 79%; but HI antibody levels of layers were high ( the antibody titers between 7 log2 to 10 log2), the qualified rate of antibody reached 98%. |
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