A total of eighty buffalo calves maintained at Livestock Production and Research Institute, Bahadurnagar, Okara were immunized againt HS vaccines. Alum precipitated HS vaccines were procured from Veterinary Research Institute (VRI), Lahore, Hira Pharmaceuticals (HPL), Lahore and Sindh Poultry Vaccine (SPy), Karachi. The oil based HS vaccine was procured from Nuclear Institute of Agriculture and Biology (NIAB), Faisalabad. The immune status of animals were studied using indirect haemaggluti nation test (lilA) and mouse protection test. The sera of the animals were examined for lilA titres on day zero (before vaccination) and thereafter on 15th, 30th, 45th, 60th, 75th and 90th day post vaccination.

All the test gave zero titre on day 0. A very poor immune response (GMT 2.1, 4.3, 2.8 and 2.1 for vaccines of NIAB, VRI, HPL and SPy, respectively) was observed on 15th day post vaccination. Maximum IHA geometric mean titres alutu precipitated vaccines of VRI, IIPL and SPV GMT 64, 64 and 52, respectively were recorded on 45th day post vaccination. Thereafter a decline in the titre commenced and titre recorded on 90th day for VRI, HPL and SPV were GMT 22.6, 22.6 and 14.9, respectively. The sera of animal vaccinated with oil based HS vaccine of NIAB showed high antibody titer than alum precipitated HS vaccines. The increase in antibody titre was gradual upto 90th day post vaccination. The IHA GMT was 73.3 on 45th day post-vaccination but titer was increased upto 90.5 on 90th day post vaccination. The sera having IHA titre of 1:16 and above protected 100% of challenged mice. The sera having titre 1:8 protected 80% challenged mice, but the scm with lilA titre 1:4 conferred no protection to the passively immunized mice. Furthermore, control animals lost their lives in response to challenge inoculum as 100% mortality was recorded. A strong relationship between IHA Litre and mouse protection test was found. The oil based HS vaccine gave better and long lasting immunity upto a period of 90 days. The alum precipitated vaccines gave a dismal picture and necessitates attempt for its improvement and switching over to other vaccines which may give long lasting immunity.