| Summary: | 碩士 === 國立屏東科技大學 === 獸醫學系 === 94 === Porcine respiratory disease complex is a multi-factorial disease which causes high mortality in pigs at the ages of 6 to 14 weeks. Cross-sectional and longitudinal bleedings of various age groups of pigs for serological examination were done in 6 pig farms in Taiwan. In addition, 17 cross-bred piglets were weaned at the age of 2 weeks, transferred to the positively pressured animal experimental facilities for the evaluation of half-life of maternal antibodies. Results showed that piglets had high maternal antibodies against pseudorabies virus ( PRV ). The antibody titers decreased as pigs grew older and dropped to its lowest level when pigs were 11 weeks old ( 0.27 ± 0.56 log2 ). The half-lives of maternally derived antibodies against PRV and PRRSV were 2.01 and 2.98 weeks, respectively. All farms were positive for porcine reproductive and respiratory syndrome virus ( PRRSV ), porcine circovirus type Ⅱ ( PCV2 ) and swine influenza virus ( SIV ) infection. The antibody titers against PRRSV and PCV2 were gradually decreased as pigs grew older and reached its lowest levels at the ages of 9 to 11 and 5 to 11 weeks, respectively. An increase of antibody titers and seropositive pigs were observed thereafter due to natural infection. Antibody profiles against SIV were different in various pig farms. All pig farms were positive for hemagglutinin 1 ( H1 ) SIV infection and four were positive for H3 SIV infection additionally. The above results indicated that the pig populations in Taiwan were commonly infected by PRV, PRRSV, PCV2 and SIV. The maternal antibodies against the aforementioned pathogens conferred a protective effect for piglets; however, loss of passive immunity at the ages of 5 to 13 weeks resulted in the susceptibility of viral infection in pigs.
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