Twelve different vaccines were prepared from hydropericardium syndrome (HPS) infected liver homogenate by using two different virus concentrations (1x10² and 1x10³ ALD₅₀) and two virus inactivants (0.1% formalin  and 0.01% binary ethyleneimine) with and with out different adjuvants. These vaccines were evaluated in 13 groups of broilers (8 in each group) for their comparative immunogenicity and protection. At day 14 of age, chicks of groups A1, B1, C1 and D1 were vaccinated with 4 oil based vaccines (OB-HPSV) with two different virus concentrations (1x10² & 1x10³ ALD₅₀) and two different inactivants (0.1% formalin  and 0.01% binary ethyleneimine), respectively. Chicks of groups A2, B2, C2 and D2 were vaccinated with 4  aluminized vaccines (AH-HPSV) using two virus concentrations and two inactivants. Similarly, chicks of groups A3, B3, C3 and D3 were vaccinated with non adjuvanted vaccines (NA-HPSV) with two virus concentrations and two inactivants. Group E was kept as unvaccinated control.  All the vaccinated birds were found sero-positive 7 days post vaccination (PV). IHA GMT results indicated no difference for different virus concentrations and different virus inactivants with same adjuvant (P>0.05). The IHA GMT recorded weekly during 0-28 days PV was the highest and more consistent (52-181) for OB-HPSV, followed by AH-HPSV (52-147) and NA-HPSV (73.3-104). The protection recorded for OB-HPSV vaccine was 100%, for AH-HPSV vaccine it 87.5% and with NA-HPSV vaccine it was 62.5% when challenged at 21 days post vaccination (PV). It was concluded that 1x10² ALD₅₀ oil based vaccines inactivated with either formalin or binary ethyleneimine can be recommended for commercial use.

Key words: Hydropericardium syndrome, ALD₅₀, oil based vaccine, alum based vaccine, protection.