Randomized controlled single-farm field evaluation of an autogenous Mycoplasma hyosynoviae bacterin: lameness treatments and exploratory serology

Mycoplasma hyosynoviae arthritis contributes to antimicrobial use and reduced welfare in fattening pig production. No commercial vaccines are available, and the efficacy of autogenous vaccines remains poorly documented. This study aimed to evaluate the effect of an autogenous M. hyosynoviae vaccine on lameness occurrence, describe M. hyosynoviae antibody profiles over time, and assess such profiles in relation to lameness development. Methods. A randomized, blinded, controlled field trial was conducted in a Norwegian fattening pig herd and its associated piglet-producing herd. Piglets received two intramuscular injections of either vaccine or saline at six and nine weeks of age. Lameness occurrence was monitored throughout the fattening period, and serum samples from a subset of pigs (n=118) were collected at 6, 8, 13, and 19–21 weeks of age for detection of M. hyosynoviae-specific IgG antibodies by T20 IgG ELISA. Data were analyzed using logistic regression models. A total of 737 pigs (383 vaccinated, 354 controls) were evaluated for lameness. The incidence of lameness treatments was 7.8% (95% CI: 5.1–10.5) in the vaccine group and 6.8% (95% CI: 4.2–9.4) in controls, with no significant difference between groups (OR=1.28, 95% CI: 0.76–2.17, p=0.354). Most lameness cases occurred during the first three weeks after arrival at the fattening farm. Vaccination was not associated with increased odds of serum IgG seropositivity by the T20 ELISA in an exploratory subset (OR=0.97, CI: 0.36–2.58, p=0.947). Antibody levels varied with sampling time; the highest levels were observed at the end of fattening. Autogenous vaccination with a Mycoplasma hyosynoviae bacterin at six and nine weeks of age was not associated with a measurable reduction in lameness treatments in this study, and vaccinated and control pigs showed similar T20 IgG ELISA antibody profiles. Results should be interpreted in light of study limitations, including diagnostic uncertainty, factors related to vaccination timing and early immune dynamics, and the exploratory nature of the serological analysis. These findings highlight the challenges of evaluating autogenous M. hyosynoviae vaccines in the field and underscore the need for further research on effective preventive strategies.