Abstract
Estimation of antigenic content (146S) of FMDV serotypes (A, O, SAT2) by sucrose density gradient (SDG) ultracentrifugation by determining the absorbance at 254 nm using ISCO520C density gradient system to produce a highly potent trivalent virus vaccine. The antigenic mass 146S (µg/ml) of serotypes (O Pan Asia2, A Iran O5 and SAT2/EGY/2012) were 6.5, 6.2 and 5.9, respectively. The vaccine was injected into three groups of calves (2individuals/each group) subcutaneously in lateral part of the neck for a dose 3 ml (6.2µg/serotype/ml), a dose 1.5 ml (4.1µg/serotype/ml) and a dose 1 ml (2µg/ml), the sera samples were collected at 7th day post vaccination (dpv), 14th dpv, 21th dpv, 28th dpv and every 2wks till 40 weeks to evaluate the immune response along that period. The antibody titers/40wpv for a 3 ml dose (6.2µg/ml) of serotypes (O Pan Asia-2, A Iran O5 and SAT-2/EGY/2012) were 2.08, 2 and 1.94, respectively (over the protective titer, PT=1.5 in SNT for cattle), a dose (4.1µg/ml) of the three serotypes were 1.56, 1.62 and 1.63 (over PT), respectively, But for (2µg/ml) dose of the three serotypes, the antibodies titer were 1.25, 1.19 and 1.2 (below PT), that show the antibodies titer depend on the concentration of the antigenic mass (146S) and with increase of the 146S concentration increase of the potency of the vaccine. The potency testing of that study depend upon the correlation between 146S and the neutralizing antibody titers were measured by SNT which are the perfect alternative of other potency tests which employ the challenge of the cattle with virulent virus. The immune response of the highly potent vaccine (4.1µg/serotype/ml and 6.2µg/serotype/ml) started early after 1st wpv and the protective titer remain for more than 38 wpv (especially in 6.2µg/ml injected calves) and that confer the potency of the vaccine of that dose.

Key words: Key Words: 146S, SDG, SNT, potency testing, trivalent highly potent FMDV vaccine.