Integrated Field Evaluation of a Caseous Lymphadenitis Vaccine and Environmental Bacteriological Profiling in Commercial Goat Farms in South Korea.

Background/Objectives: Caseous lymphadenitis (CLA), caused by Corynebacterium pseudotuberculosis, is difficult to control on goat farms because of subclinical infection, abscess rupture, environmental contamination, and repeated herd-level exposure. This study evaluated a Korean inactivated CLA vaccine under commercial goat farm conditions and combined vaccination outcomes with farm-level bacteriological profiling. Methods: Goats from three commercial farms were allocated according to baseline CLA serostatus and vaccination status into seropositive vaccinated, seronegative vaccinated, seropositive non-vaccinated, and seronegative non-vaccinated control groups. Vaccinated goats received two intramuscular doses at weeks 0 and 4. Clinical signs, external abscess occurrence, growth performance, CLA-specific antibody responses, and abscess bacterial loads were monitored. Farm-level microbial profiles were assessed using culture, MALDI-TOF MS, and targeted PCR. Results: Baseline antibody classification showed strong agreement between the commercial CLA ELISA and the in-house whole-bacterial IgG ELISA, with a Spearman's rho of 0.89 (p < 0.001) and 96.7% classification agreement. Vaccination induced CLA-specific antibody responses in both assays and was not associated with a persistent reduction in growth performance. External abscesses were observed only in baseline seropositive goats. Abscesses occurred in 1/30 vaccinated and 2/15 non-vaccinated seropositive goats, but the difference was not statistically significant (p = 0.254). Microbial profiling showed farm-dependent detection patterns. Conclusions: The vaccine induced CLA-specific antibody responses (immunogenicity) with acceptable tolerability. The exploratory abscess endpoint was underpowered, and clinical protection was not confirmed; larger studies are needed.