Evaluating the Effectiveness of Probiotic and Multivalent Vaccination Strategies in Mitigating Bacterial Chondronecrosis with Osteomyelitis Lameness Using a Hybrid Challenge Model

Bacterial chondronecrosis with osteomyelitis (BCO) is caused by several bacteria, including <i>Salmonella</i>, <i>Staphylococcus</i> spp., <i>Escherichia coli</i>, <i>Enterococcus</i> spp., and <i>Mycoplasma</i> spp., and BCO is a significant animal health and welfare issue in broiler production, causing 1-2% of bird condemnation at marketing age and resulting in annual losses of tens of millions of dollars. This study evaluated the efficacy of a probiotic program alone and combined with a multivalent electron beam (eBeam)-inactivated vaccine in reducing BCO lameness. The probiotic program included an <i>Enterococcus faecium</i> spray (<i>E. faecium</i> 669, at 2 × 10⁹ CFU/bird) at hatch and a triple-strain <i>Bacillus</i>-based product (<i>B. subtilis</i> 597, <i>B. subtilis</i> 600, and <i>B. amyloliquefaciens</i> 516 at 1 × 10⁹ CFU/bird/day) in drinking water from day 1 to day 56. An aerosol transmission challenge model simulated commercial bacterial exposure. Birds were divided into five groups: a positive control (PC) group (T1) and a negative control (NC) group (T2) receiving no treatment and three treatment groups receiving the probiotic program (T3), the multivalent vaccine (T4), or both the probiotic program and the multivalent vaccine (T5). Data analyzed via ANOVA (<i>p</i> < 0.05) showed T3, T4, and T5 had significantly lower lameness (43.7%, 40.3%, and 40.7%) than T2 (71.0%) and T1 (83.0%). T5 resulted in reductions comparable to T4, indicating no significant synergistic effect. These findings show that probiotics alone or with a vaccine effectively mitigate BCO lameness, enhance broiler welfare, and reduce economic losses.