The objective of this study was to evaluate the effects of corn silage (CS) type and monensin supplementation throughout the transition period on metabolism and performance. Multiparous Holstein cows (n = 85) were enrolled 28 d before expected parturition and randomly assigned to treatments in 2 × 2 factorial arrangement with diets containing conventional (CON) or brown midrib (BMR) CS, with monensin (M; 330 mg/d prepartum and 450 mg/d postpartum) or without M (NO; 0 mg/d). Diets were formulated to be identical except for CS type and small inclusion mix delivering M or NO. Prepartum diets, CON (41.6% NDF, 17.8% starch, 94.3 g/kg DM MP) and BMR (40.8% NDF, 17.3% starch, 95.9 g/kg DM MP), were fed from −21 d through calving. Postpartum diets, CON (30.3% NDF, 27.8% starch, 116.6 g/kg DM MP) and BMR (29.2% NDF, 27.7% starch, 118.1 g/kg DM MP), were fed from calving through 42 d in milk. Blood samples were taken 1×/wk prepartum, 2×/wk for wk 1 and 2, and 1×/wk through wk 6 postpartum. Repeated measures data were analyzed using PROC MIXED in SAS with main effects of treatments and time (T), and all interactions. Prepartum and postpartum data were analyzed separately. Prepartum dry matter intake (DMI) was higher for cows fed BMR than CON (14.7 vs. 14.0 kg/d; P = 0.03), whereas cows fed M had lower intake than cows fed NO (13.9 vs. 14.8 kg/d; P < 0.01). Postpartum DMI was not different. A 3-way interaction of CS, M, and T was observed for milk yield (P = 0.02) where BMR-M was highest and CON-NO lowest during wk 5 and 6 postpartum. A CS × T interaction was observed such that NEFA in wk −2 and −1 (P < 0.02) and BHBA in wk 5 and 6 postpartum (P = 0.01) were lower for cows fed BMR than those fed CON. Cows fed M had lower BHBA than cows fed NO both prepartum (P = 0.04) and postpartum (P = 0.01). Postpartum, cows fed BMR had lower NEFA than cows fed CON (P = 0.01). Cows fed BMR and cows fed M throughout the transition period exhibited improvements in performance and metabolism in the prepartum period, with a possible synergistic effect of CS and M supplementation on milk yield.