Forty serum samples were screended from vaccinated white pekin ducks for the duck hepatitis virus (DHV) antibody level after they had received a single dose or two doses of the vaccine. The results of serological examination using indirect haemagglutination test (IHA), serum neutralization test (SNT) as well as agar gel precipitation test (AGP) revealed that: (1) For the IHA test the purified and concentrated infected embryo antigen of DHV was adsorbed to sheep red cell using one of 3 sensitizing agents at different dilutions. Preliminary tests on sera of unvaccinated and experimentally vaccinated ducks showed that the best dilution of either tannic acid and chromic chloride was 1:20 000 for desensitization while
de EETTERE that of gluteraldehyde was 1:100. Chromic chloride was also found to be the best of the 3 agents while gluteraldehyde was the least one. The antibodies in the sera of ducks vaccinated twice were found by the IHA test to be of higher titers than those in the sera of ducks vaccinated once. (2) The DHV neutralizing antibodies could be detected in the vaccinated duck sera using the SNT. The neutralization indices (NI) were higher in flocks which were vaccinated with two doses of the vaccine as it reached 4 - 7.3 whereas in case of ducks vaccinated with single dose the NI was 1.2 - 6.3. (3) The AGP test gave clear precipitating lines when testing sera of high antibody level while sera of NI ranging from 1.2-2.7 failed to produce these DD FELT lines against DHV antigen. (4) The agarose
o electrophoresis of the plasma protein of unvaccinated and vaccinated ducks showed a correlation between the gammaglobulin and antibody titer detected by IHA and SN tests.
SNT.