Recent studies with dry and lactating cows subjected to heat stress while fed OmniGen-AF (OG, Phibro Animal Health, Teaneck, NJ) were reported to have lower respiration rates and rectal temperatures than non-supplemented controls. In addition, dry matter intakes were maintained, SCC and health events were lower and milk yields were higher in the cows fed OG. In this study we evaluated the effects of feeding OmniGen-AF (OG) or placebo control (CON) during the dry period and early lactation on milk yield of dairy cows. We hypothesized that feeding OG during the dry period and through the second breeding (~150 d) would improve milk yield and fertility of cows, by promoting improvements in immune status and health. The study was conducted from July 2018 through February 2019 on a commercial dairy in Florida, with cows exposed to high THI during the dry period. To test our hypothesis, cows were fed OG (56 g/h/d; n = 140) or CON (56 g/h/d placebo; n = 132) during the dry period (~60 d) and were supplemented until pregnancy confirmation or the second breeding (~210 d total feeding length). In each treatment, cows were fed as a group and average dry matter intake (DMI) of cows fed OG and CON was recorded during the dry period and lactation. Daily milk yield was measured once each week, starting at the second week of lactation. Data were analyzed using MIXED procedure in SAS with weeks in milk (first 9 weeks) as repeated measurement and parity as covariate. Production results reveal that cows receiving OG had greater milk yield relative to CON cows (OG = 40.6 ± 0.76 kg/d, CON = 38.5 ± 0.68; P < 0.05). During lactation, no treatment differences were detected in DMI (OG = 26.1 ± 3.41 vs. CON = 25.6 ± 3.77 kg/d). Analysis of metritis, mastitis, retained placenta, laminitis, ketosis, pneumonia, and displaced abomasum frequencies and fertility will be performed as cows complete the trial. In conclusion, OG supplementation during the dry period and early lactation increased the milk production in dairy cows, which may indicate improved health status.