| Summary |
Fifty-seven piglets, farrowed by the vaccinated sows in a hog cholera free pig farm, were divided into four groups. The first group was consisted of 16 neonates, were vaccinated with a dose of LPCV vaccine each time at one day old and at 3 and 6 weeks of age. The 15 piglets in the second group were vaccinated two times at 3 and 6 weeks of age. For the third group, 13 piglets were only vaccinated at 6 weeks old. The other 13 piglets in the fourth group were vaccinated two times at 6 and 9 weeks of age. After vaccination, all the pigs in the four groups induced active immunity and serum neutralization antibodies could last to 6 monthes old. The geometric means of serum neutalization titer at 6 monthes of age, tested with END method, were 29 X, 93 X, 256 X and 265 X, respectively. The result showed that the earlier vaccination of piglets the lower antibody was lasted to 6 monthes for market.
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