Foot and Mouth Disease (FMD) vaccine evaluation required viral challenge of vaccinated cattle. Difficulties of potency testing include finding animals FMDV antibodies free and the challenge should be conducting in high containments. Alternative approaches, such as Serum Neutralization Test (SNT) and antigen concentration (146S) were developed. In this study, antigen dose, SNT, and animal challenge were evaluated after a single dose. Three vaccine batches with different antigen doses of inactivated trivalent FMD vaccine prepared from Egyptian strains (serotypes A, O, and SAT2) were evaluated. Calves 6-8 month old were vaccinated with 2ml of the vaccine, sera collected at 28 days post vaccination and animals were challenged with 10⁴ BID₅₀ of homologous FMDV strains via intra-dermolingual route.  All the antigen doses induced SN protective titers with the exception of one animal in each of the serotype O batch-2 (3.1µg/dose) and serotype SAT2 batch-1 (2.7µg/dose) which showed 0.9 log10 SN titers. All animals were completely protected against challenge with serotype A in all tested batches. Serotype O batch-1 and 3 (2.5 and 5µg/dose) induced a complete protection; however, batch-2 (3.1µg/dose) showed 80% protection. In serotype SAT2 challenge, the lowest dose of 2.7µg/dose showed 80% protection meanwhile other doses of 3.3 and 5.4µg/dose completely protected the animals. In both serotypes O and SAT2, feet lesions were observed in the calves that showed the lowest SNT levels (0.9log10). In conclusion, the study results indicate that 146S particles concentration (3.3, 2.5 and 1.4 µg) for serotypes SAT2; O and A, respectively can be used for vaccine formulation. Additionally, both SNT and 146S particles concentration could be suggested as an alternative method for vaccine evaluation.

Key words: 146S content, Challenge, FMDV, SNT, Vaccine