FIG. 3.

High uterine inoculum and cohort challenge with C. abortus and low prechallenge anti-C. abortus serum IgM levels are associated with reduced fertility in heifers previously exposed to C. abortus. Pregnancy as an indicator of fertility was evaluated 6 weeks after uterine challenge with C. abortus. (A) Overall pregnancy data for Holstein heifers (n = 30) inoculated in the uterus with 0, 10⁴, 10⁵, 10⁶, or 10⁸ IFU (with or without cohort challenge). (B) Pregnancy data for the same group of 30 heifers, with high (above-median) or low (below-median) prechallenge anti-C. abortus IgM levels. Taken together, these data suggest that reduction of bovine fertility by reinfection with C. abortus depends on the epidemiological parameters of herd infection with C. abortus (specifically, on the total challenge) via direct uterine inoculation and via cohort exposure and the immune response to previous infection.