We determined the effects of supplementation of a ruminally protected lipid (Megalac-R, Church & Dwight Co., Princeton, NJ) on subsequent beef cow reproductive performance. Sixty primiparous cows (428 ± 42 kg of BW) were used in a completely randomized design. Cows were stratified by breed, BCS and the previous year’s calving date, and assigned to one of 2 treatments: control (CTRL; 1.36 kg·d⁻¹ of corn gluten feed) and treatment (MLAC; 1.36 kg·d⁻¹ of corn gluten feed and 0.23 kg·d⁻¹ of Megalac-R). Cows grazed a mixed winter forage pasture of rye (Secale cereale) and ryegrass (Lolium multiflorum) and had ad libitum access to water. Supplementation of CTRL and MLAC occurred from 30 d before AI until 7 d post-AI. Daily, cows were individually penned and received their respective supplementation. Cow BW and BCS were recorded 35 and 28 d before AI and 35 and 60 d after AI. At initiation of the breeding season cows were exposed to the 7-d CO-Synch+CIDR ovulation synchronization protocol. Pregnancy was diagnosed on d 30, 60, and 90 after AI. Cows pregnant to AI were monitored until calving to determine length of gestation and calf birth weight. Treatment did not affect (P > 0.05) mean cow BW (491 ± 2.9 kg) or change in cow BW. There was no effect (P > 0.05) of treatment on pregnancy rates to AI (53 ± 0.5%) or at 90 d after AI (94.5 ± 0.5%). Length of gestation was greater (P = 0.0234) for MLAC (285 ± 1.3 d) than for CTRL (281 ± 1.1 d). No effect of treatment was observed for calf birth weight (34 ± 3 kg; P > 0.05). Supplementation of 0.23 kg·d⁻¹ of a ruminally protected lipid to primiparous cows did not enhance subsequent cow reproductive performance.