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The efficies of both live and killed Newcastle disease vaccine have lxen discussed by many oultrymen and researchers for a long time. The Institute prcduced a Newcastle disease live vaccine in 1 9, however, some disadvantages were encount ered in the field buause the pcultrymen were lack of knowledges for the usage of the vaccine, the proper time of vaccination, and the environment of x’ulty farms. Therefore, tissieculture Newcastle vaccine was duced again by DD and DK cultrue from original strain. The DK stain was purified from the original stain by the methcd of ceilplapue cloning toohnirpie, The effect of vaccination with tissue-culture Newcastle disease vaccine on chickens was evaluatoi in SQCU) thickens of different ages. The resulis were summarimi as follows:
1 The tissue-culture DK stuain of Newcastle disease vaccine administered renterally was gccd for all ages of chickens, esiaUy, the HI tier were under x20 in growing and and adult chickens, No adverse effect on egg prcduction and hatchility was noed. The HI titer value increased from 13.4 to 24? in 2 weeks after vaccination. It oould maintain this values for 6-9 months, them decreased to x22 gradually. When p-opt re-vaccination was carried out at this time, it could restore the HI titer up to x22? within 2 weeks after inctulation.
2.Newcastle disease vaccine preduced from DD stain had low virulence and safely Smnniary although it prcduced low HI titer and the HI titer would start to decrease at one month after vaccination, it still gccd for keby chicks. In this cases, the chicks mustkerevaccinaed using DK strain vaccine to restore proper HI tia
3.Two successive dores ofD K stain vaccine in drinking water were given, but could not obtain desirable HI tiers. The survived rates were botween 50 and 70% following challenge.
4 The chicks must ke vaccinated when the acquired maternal antibody has disappeared to ro, kecause some indicated that the production of antibody by vaccination would ke disturked by natural antibody.
5.Although the buby chicks could ke vaccinated using DK stain vaccine when the acquired antibody decreased to nothing to obtain desirable immunity; small jert of chicks showed undesirable reactions such as lccs of appetite and greenish diarrhea within 4-? days after vaccination. Therefore, the first vaccination should ke performed by usingDD stain vaccine andbr DKstain vaccineindriniting water for two successive dcces, then, used DK staine vaccine as 1xGter shot 6. It is advisadle that theHltiermustketitratedkeforevaccination. IftheHltitervalueisoverX40,itis not necessary to vaccinate the chickens against this disease.
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