Effects of feeding OmniGen-AF (OG) to bred heifers and cows in 3 separate trials in a university dairy herd was summarized. In trial 1, 15 heifers received OG beginning at 6 months of age through day of calving; 18 animals served as controls. In trial 2, 35 heifers received OG beginning 60 d prior calving through day of calving; 38 animals served as controls. In trial 3, 11 late lactation cows received OG beginning 60 d prior to dry-off through 30 d post calving; 11 controls received OG at dry-off through 30 d post calving. OG was fed at 9g/100 kg BW/d. Prior to and/or during each trial, quarter milk samples were collected for microbiological analyses and SCC to monitor mastitis status. Mastitis treatments were recorded, and DHIA records monitored for milk production and cow longevity. Data were analyzed as Control vs. Treatment using ANOVA and means separation with Least Squared Means (PROC GLM, SAS 9.4, 2017). Results demonstrated that for heifers in trials 1 and 2, controls exhibited a greater number of clinical mastitis quarters than OG heifers during the precalving period (12 vs. 9). Likewise, after calving through dry-off for all trials, controls exhibited a greater number of clinical mastitis quarters than OG animals (7 vs. 0). Across all trials, 11 quarters from controls were treated for mastitis, whereas no OG animals were treated. Eleven control quarters became chronically infected, while only 2 OG quarters became chronic. At dry-off, the number of mastitis cases present in control and OG animals were 7 and 2. Numbers of quarters from control and OG animals diagnosed with new IMI between calving and dry-off were 4 and 0. DHIA overall lactation SCS were 3.04 and 2.48 for control and OG animals (P<0.10), and lactation SCC were 209,000/ml and 121,000/ml for control and OG animals (P<0.14). The 305-d ME for milk yield were 11,020 and 11,286 kg for control and OG animals. The 305-d ME for fat was numerically higher for control than OG animals (415 vs. 409 kg), and protein was numerically lower (317 vs. 324 kg). Cull rates were 10.52% for controls and 5.88% for OG animals. OG is effective in maintaining udder health and lowering SCC in dairy cattle when fed at least 2 months prior to calving.