| Classical Swine Fever (CSF), one of the important porcine infectious diseases, which is highly contagious and lethal, causes great harm to the health of pigs and development of swine industry. With the wide use of Hog Cholera Lapinized Virus Vaccine in China, CSF pandemic has been effectively controlled to a certain degree. However, in recent years, CSF characterized with chronic and atypical features emerges constantly in China, with an increasingly complex trend. Determining scientific and reasonable immunization program and monitoring the antibody level in herds of swine have become the crucial prevention measures towards CSF in large-scale pig farms. In this study, the whole immunity situations of pigs towards CSF in11large-scale pig farms subordinated to three husbandry companies in Guangxi province from2011to2012have been investigated. Based on the investigation, the research on the law of decreasing and increasing of maternal antibodies and optimization experiment on initial immunization age in piglets have been carried out as well. According to the results of these experiments, we can know about partial immunity situation of piglets towards CSF in large-scale pig farms in Guangxi province. And it also provides scientific reference for establishment of CSF immunization program, the optimization of initial immunization age, and preventing and controlling of CSF effectively. This study includes two major parts:In the first experiment.6910serum samples from the11large-scale pig farms subordinated to three husbandry companies from2011to2012(3293from2011and3617from2012, respectively) were tested on CSF antibody by using ELISA. The average positive rates of all of three husbandry companies was66.45%in2011and83.17%in2012. which indicated that the CSF antibody level of husbandry companies from2011were not ideal, however, they have been improved significantly in2012, especially the CSF antibody level of Husbandry Company C which increased most rapidly with average antibody positive rate from61.06%in2011to86.20%in2012. Based on the investigation of CSF antibody level of pigs in six different biophysical and feeding stages (suckling pigs, weaned pigs, finishing pigs, replacement gilts, breeding sows and stock boars), it manifested the antibody level of suckling pigs, stock boars, replacement gilts, and finishing pigs were more ideal than other pigs in these three husbandry companies and the lowest for weaned pigs. According to the investigation of immunization programs in all of three husbandry companies, it demonstrated that with similar immunization programs the difference between CSF antibody level induced by CSF cell vaccine used by Husbandry Company A and that induced by CSF rabbit spleen-lymph tissue vaccine used by Husbandry Company C was not significant. Husbandry Company B adopts CSF ultra pre-immunity, and its suckling piglets’ average positive rate was91.61%, significantly greater than the other two husbandry companies that did not implement CSF ultra pre-immunity. Difference between CSF antibody positive rate of sows in Husbandry Company B adopting general immunization for twice a year and Husbandry Company A and C implementing immunization process of postpartum sows20d after parturition was not significant, while the result of CSF antibody levels of sows for1st,2nd,3rd,4th,5th or higher parity showed that CSF antibody levels of sows decreased with the increasing of parity after5th.In the second experiment, the research on decreasing and increasing of maternal antibodies were investigated by using ELISA method. The results showed that the maternal antibodies titer of88neonatal piglets without breast-feeding from Husbandry Company C was20. After lactation, maternal antibody blocking values reached to its maximum in its first day, and the piglets at age of1-14days showed higher level of antibody titer with210. After14days of age, blocking rate of CSF maternal antibody in piglets and its corresponding antibody titer were both obviously declined, and in14to28days, the antibody level dropped rapidly. When at35days of age, the immunity of61.36%(54/88) of piglets had dropped to the level under protection boundary, and the titer of maternal antibody dropped to20at42days of age. Overall, the CSF maternal antibody of piglets began to decrease with the increase of age of piglets after the age of14days in Husbandry Company C. and the antibody titer had arrived to20at42days of age. Based on research on law of decreasing and increasing of maternal antibodies levels in Husbandry Company C, four groups with four different initial immunization age(14d,21d,28d, and35d of piglets, respectively) were set. The antibody blocking rate of the group of piglets whose initial immunization age are at28d increased from42.82%before the immunization to66.34%a week after initial immunization and it went up to79.58%two weeks after initial immunization. The immune efficacy of the group with initial immunization age at28d is apparently better than other groups, thus, it is suggested that the best date of CSF initial immunization is at28days of age in Husbandry Company C. |
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