Current potency assay of bovine respiratory viral vaccines is routinely focused on vaccination antibody assay model in
susceptiblecattle. Based on the published data among validity of rabbits as a laboratory animals that could be used to
evaluate potency of many veterinary vaccines and difficulty in finding seronegative cattle to be used in potency assay of
bovine respiratory viral vaccines plus the need to carry batch to batch release potency test in less expensive way, The
present study was undertaken to address utility of rabbits for relative potency assay of a combined inactivated vaccine of
IBR, BVD,PI3 and BRS viruses in comparison with susceptible calves.Each of two batches of the local vaccine and one
imported vaccine was inoculated intramuscularly twice 14 days apart into one group of three seronegative cattle calves
using its recommended dose, and one group of five adult bosket rabbits using 2/5 cattle dose of each vaccine.The test
vaccine dose dependent immune response assays in calves and rabbits were conducted by inoculation of each of 1/2, 1/4
and 1/8 the full dose of the tested vaccine in one group of each calves and rabbits. Serum samples were collected and
measured by serum neutralization test. The tested vaccines were induced mean neutralizing antibody titer averages of
(1.05 - 1.5), (1.5 - 1.56), (1.05 - 1.64) and (1.42 - 1.52)log₁₀ in sera of immunized rabbits for BVD, IBR, PI-3 and BRS
viruses respectively,and (1.65 - 1.75),(1.5 - 1.8), (1.44 - 1.9) and (1.6 - 1.65)log10 in sera of vaccinated calves for the same
viruses respectively by the 3^th weekafter boostering; test vaccines seem to be potent in calves and immunogenic in
rabbits.Averages of the Relative Potency ( RP ) that determined by dividing each mean virus neutralization antibody titer
of log10in sera of the immunized rabbits by that of the vaccinated calves were (0.6 - 0.8), (0.8 - 1.0), (0.5 - 0.8) and (0.8 -
0.9) for each of BVD, IBR, PI3 and BRS viruses respectively by the 3^th weekafter boostering. However, the results of the
vaccine dose dependent-immune response in both of immunized rabbits and vaccinated calves are proved the sensitivity
of rabbits in parallel with calves to the reduced doses of one of the tested vaccines; the reduced doses of the vaccine were
induced a considerable regressed antibody titers in serum of immunized rabbits as in vaccinated calves. In conclusion,
the present data indicate that the rabbits constitute as useful suggestive laboratory animals for potency evaluation of the
bovine combined respiratory inactivated viral vaccines instead of cattle calves