Three hundred sixty-one multiparous late lactation cows were selected using DC305 and randomly assigned to 1 or 2 diet additives before dry-off; basal diet + placebo (PL, n = 181) or basal diet + OmniGen-AF(OG, n = 180). Diet groups were balanced by parity, DIM, calving date, 305ME, milk and health history. Both additives were fed at 56g/h/d, added directly to the dry and lactation TMR’s. Cows were fed the assigned diet additives from dry-off through 120 d in milk (DIM) and health, milk, milk quality and reproduction evaluated. Data were analyzed by PROC GLM with significance tested at P < 0.05 and only cows completing 120 DIM were included. Average parity and days dry for cows fed the PL and OG were 3.7, 59.3 d and 3.6, 58.3 d, respectively. Cows fed OG had fewer retained placenta (−6.6%, P = 0.023) and metritis (−5%, P = 0.044) cases than PL fed cows. Mastitis cases were similar, however cows fed OG tended to have fewer repeat cases (P = 0.107). No differences were detected in the other recorded health metrics. Individual milk and milk components were recorded and were used to calculate week-4 milk (W4), energy and fat corrected milks (ECM, FCM). No differences were detected between PL and OG fed cows for test-day (TD) milk 1–4 (44.6kg vs. 45.5kg), W4 (43.5kg vs. 44.7kg) or peak milk (49.9kg vs. 50.4kg). OG fed cows produced more ECM (+1.5kg, P = 0.008) and FCM (+1.7kg, P = 0.007) through TD 1–4 than PL cows. OG cows had higher % milk fat (MF) at TD 1 (+0.3) and kg MF at TD 1 (+0.13), 2 (+0.09) and 3 (+0.09) and 0.05 kg more milk protein (MP) at TD 2 than PL cows. Compared with PL, the OG cows made milk with more kg MF (1.5 vs. 1.6, P = 0.002), kg MP (1.3 vs. 1.5, P = 0.053) and % MF (3.45 vs. 3.56, P = 0.032). TD 1–4 SCC’s were not different. All reproductive measures were not different, however OG cows tended to have fewer days to first breeding (P = 0.12) and greater days carried calf (P = 0.088) than PL cows. In conclusion, feeding OG to multiparous cows from dry-off through 120 DIM resulted in differences in peripartum disease incidence, milk and milk components.