Passive transmission of Campylobacter fetus by immunised bulls

Two groups of 24 heifers were mated with 3 immunised and 3 susceptible bulls respectively. Six heifers in each group were infected artificially with Campylobacter fetus sub-sp. fetus biotype venerealis. Among susceptible heifers mated with immunised bulls, 13/18 became pregnant and 5/18 yielded evidence of infection with C. fetus. Among susceptible heifers mated with susceptible bulls, 7/18 became pregnant and 10/18 yielded evidence of infection. C. fetus was isolated on one occasion from an immunised bull, but the immunised bulls failed to develop carrier status and one was shown to be refractory to artificial challenge. Susceptible bulls developed carrier status during the breeding period. It is suggested that passive transmission of C. fetus by immunised bulls can occur under conditions of intensive sexual activity.