Development of a bacterin–toxoid vaccine using a Korean isolate for protection against caseous lymphadenitis in goats

Caseous lymphadenitis (CLA), a chronic infectious disease caused by Corynebacterium pseudotuberculosis, remains a major concern in small ruminant populations owing to its persistent nature and impact on animal productivity. Despite the availability of commercial vaccines, their efficacy in goats has been inconsistent and field-based evidence supporting their use remains limited. In this study, we report the development and evaluation of a novel bacterin-toxoid vaccine formulated with C. pseudotuberculosis strain 51-12A obtained from a Korean native goat. The toxoid, prepared from culture supernatant and enriched with immunoreactive proteins such as PLD, CP40, NanH, and PknG, was combined with formalin-inactivated bacterin to formulate a dual-component vaccine. Immunization trials in 3-4-month-old goats demonstrated that animals receiving the combined vaccine mounted strong anti-PLD responses (optical density, OD; OD ≥ 1.0), exhibited complete protection against experimental challenge with 1 × 10⁶ colony-forming units (CFU)/mL of homologous strain, and showed no evidence of internal abscesses. In addition, field studies conducted at three independent farms confirmed the safety and immunogenicity of the vaccine under practical conditions. Vaccinated animals maintained elevated antibody titers and remained clinically healthy, while unvaccinated controls developed CLA-associated abscesses. Comparable immune responses observed in sheep suggest potential cross-species applicability. These findings highlight the efficacy and field suitability of this goat-adapted vaccine and support its potential role in CLA control strategies for small ruminant production systems.