Yeast culture products have been used in the dairy industry to modify the rumen environment of lactating cows to improve production and reduce metabolic stresses in the transition period. The objective of this study was to determine the effects of feeding Saccharomyces cerevisiae fermentation products (Diamond V Original XPC™ and NutriTek^®) on the production and health of cows from -26 thru 28 DIM. Multiparous Holstein cows (n = 100) were randomly assigned one of four top-dress treatments that were combinations of the products and ground corn to equal 50 g/d: 1) control, ground corn (CON); 2) 14 g XPC mix (XPC); 3) lower level, 19 g, NutriTek mix (NTL); or 4) higher level, 38 g, NutriTek mix (NTH). Cows were milked 3x/d and milk production and components were summarized by week. Blood samples were collected prepartum based on expected calving date at -26, -17, -14, -10, -7, -4 and -1 d, and postpartum at calving and 1, 3, 5, 7, 10, 14, 17, and 21 d for analysis of blood metabolites. Phagocytosis (PN/PM) and oxidative burst (OBN/OBM) activity of neutrophils (N) and monocytes (M) were used to evaluate immune status at -17, -7, 5, 14, and 28 d. Intake did not differ significantly among treatments through d 28, but cows supplemented with XPC or NTH tended to have greater ECM yield in this period (trt x time, P = 0.06) when compared with the other treatments (CON: 44.3 kg/d; XPC: 45.0 kg/d; NTL: 44.1 kg/d; NTH: 46.9 kg/d). Most blood metabolites and minerals were not different among treatments. Activities of PN (Trt, P = 0.01) and OBN (Trt, P < 0.01) were increased at d 5 for cows supplemented with NTH when compared to cows given CON or NTL, (CON: 53%, 44%; XPC: 58%, 49%; NTL: 53%, 48%; NTH: 64%, 58%). While cows supplemented with NTL appeared to partition more energy toward other metabolic uses than milk production, the difference of innate immune system activity during the first week of lactation and the differences in ECM production shows a possible benefit of supplementing XPC or NTH to transition dairy cows.