In order to evaluate the efficacy of inactivated oil-emulsion Newcastle disease vaccine (commercially available on market in Serbia) we carried out the potency test in chickens, using hemagglutination inhibition (HI) test for detection of antibodies. Th e values of HI titers in the serum before and three weeks aft er vaccination revealed immunoconversion (IC) in chickens, and indicated potential diff erences in the immunoconversion values between two groups vaccinated with monovalent and polyvalent vaccine. In the period 2010-2012, 27 vaccines were tested, there of 21 polyvalent and six monovalent ones. Th ree weeks aft er the vaccination, HI titers of all vaccines were high. Th e average IC values were calculated as log2 (HI titer). The values ranged from 2.2 to 8.2 for polyvalent vaccine, whereas average values for monovalent vaccines were in the range from 3.2 to 6.3. Three weeks post vaccination; no statistically signifi cant diff erences were recorded in the immune response between the tested groups of birds (vaccinated with monovalent and polyvalent vaccines). This supports the fact that both tested vaccines demonstrated good potency to creating immunity against ND in vaccinated birds.
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