Assessment of immunization procedures for foot-and-mouth disease in large-scale pig farms in China based on actual data and dynamics

Foot-and-mouth disease(FMD)is an acute,highly infectious and pathogenic animal disease.In recent years,with the rapid development of the swine breeding industry in China,pig farms have shown a trend of larger-scale development.Large-scale pig farms employ standardized management,a high level of automation,and a strict_system.However,these farms have a large trading volume,and increased transmission intensity of FMD is noted inside the farm.At present,the main control measure against FMD is pig vaccination.However,a standard for immunization procedures is not available,and currently adopted immunization procedures have not been effectively and systematically evaluated.Taking a typical large-scale pig farm in China as the research subject and considering the breeding pattern,piggery structure,age structure and immunization procedures,an individual-based state probability model is established to evaluate the effectiveness of the immune procedure.Based on numerical simulation,it is concluded that the optimal immunization program involves primary immunization at 40 days of age and secondary immunization at 80 days of age for commercial pigs.Breeding boars and breeding sows are immunized 4 times a year,and reserve pigs are immunized at 169 and 259 days of age.According to the theoretical analysis,the average control reproduction number of individuals under the optimal immunization procedure in the farm is 0.4927.In the absence of immunization,the average is 1.7498,indicating that the epidemic cannot be controlled without immunization procedures.

Study on Antibody Dynamics against Porcine Contagious Pleuropneumonia in Piglets

In order to provide basis for establishing a scientific and reasonable immune procedure against porcine contagious pleuropneumonia in pig farms, antibody dynamics in piglets inoculated with two vaccines against porcine contagious pleuropneumonia （ APP-1,2, 7 ） were detected. The result showed that average antibody blocking rate and antibody positive rate in piglets inoculated with two vaccines against porcine contagious pleuropneumonia exhibited similar variation trend. At 21 day after primary vaccination, average antibody blocking rate and antibody positive rate against porcine contagious pleuropneumonia in piglets reached the peak and then declined gradually. After secondary vaccination, average antibody blocking rate and antibody positive rate against porcine contagious pleuropneumonia in piglets increased gradually, which reached the second peak at 30 day after secondary vaccination （60 day after primary vaccination） ; subsequently, average antibody blocking rate declined gradually but still remained at a high level; antibody positive rate had little change. Average antibody blocking rate against APP-1 was slightly lower than the critical level of antibody protection at 44 day after primary vaccination ; antibody positive rate was slightly higher than the qualification rate at 37 day after primary vaccination; average antibody blocking rate against APP-7 was close to the critical level of antibody protection at 30 day after primary vaccina- tion, suggesting that piglets should be inoculated twice with polyvaccine against porcine contagious pleuropneumonia during the entire growth period, and the secondary vaccination should be performed at 30 -37 day after primary vaccination.