CD40LG and chlamydia trachomatis infectious disease: The detection of IgM antibodies against C. pecorum in every single calf over the study period is consistent with the ubiquitous presence of C. pecorum in the herd and the highly efficient colostral transfer of maternal IgM antibodies to the calf, the short 4-day half-life of these antibodies in the calf, and the calf's own emerging IgM response to the chlamydial infection [24], [38], [39], [40].