This study examines the effects of vaccination and medication on bacterial contamination in milk and evaluates the potential of ozone technology for bacterial reduction. A total of 52 milk samples were collected, representing 26 paired observations analyzed statistically from dairy cows aged 2–9 years in Subang, West Java, were analyzed before and after ozonation. Bacterial counts were assessed for compliance with SNI 3141.1:2011. Non-parametric statistical methods were applied because the microbial data did not follow a normal distribution, as indicated by Shapiro-Wilk and Kolmogorov-Smirnov normality tests (p < 0.05). After ozonation, a statistically significant reduction in bacterial counts was observed. Paired analysis using the Wilcoxon Signed-Rank test (paired N = 26) showed a significant decrease in Total Plate Count (Z = 4.198, p < 0.001), with a large effect size (r = 0.82). Mean TPC decreased from 6.07 × 10⁸ CFU/mL (log₁₀ = 8.78) before treatment to 1.68 × 10⁷ CFU/mL (log₁₀ = 7.23) after 15 minutes of ozonation, corresponding to an average reduction of 1.55 log₁₀ CFU/mL. Following ozonation, compliance with SNI 3141.1:2011 increased from 3.8% to 26.9%. These findings demonstrate that ozone treatment effectively improves the microbiological quality milk from vaccinated and medicated dairy cows and can serve as a residue-free post- harvest intervention to enhance milk safety and quality in herds that are undergoing therapeutic treatments.