Abstract   

Hunioral immune responses against Hydropericardium syndrome (HPS) were measured in broilers tbllowmg single vaccination With a commercial oil-based vaccine, three commercial fonnalized inactivated and one self prepared formalized inactivated vaccine and correlated with challenge protection. In all vaccinated groups, 100 per cent birds became seropositive eight days post vaccination on indirect haernagglutinanon test (76-128). Non significant difference was observed in groups given formalized vaccines, that peaked (512) on day 16 and showed decreasing trend (153-256) from day 32 to 38. Whereas in case of oil-based vaccine titre was still higher (307). Non vaccinated groups could not survive the challenge and there was 100 per cent mortality in this group. Single shot of formalized inactivated vaccines gave protection, about 80 per cent in challenged groups, whereas booster dose of formalized inactivated vaccine gave about 97 per cent protection in challenged groups. Single shot of oil-based vaccine gave best protection that was up to 98.5 per cent. It was concluded that oil- based vaccine was best due to sinnle shot and long