|Abstract:||Spring-calving, mature Angus, Simmental, and Simmental x Angus cows (n = 191) were utilized to evaluate the effects of prepartum diet type on cow and subsequent calf performance. Cows were blocked by BW and calving date into 16 pens and allotted to isocaloric, isonitrogenous dietary treatments: corn coproducts and ground cornstalks (COP) or ground hay (Hay). Treatment diets were fed from 90d prepartum to calving. All cows were fed a common diet postpartum. Cow BW and BCS were taken at beginning of feeding period, calving, and breeding. Calf BW was taken at birth and 56d intervals from the average calving date. Milk production was determined utilizing the weigh-suckle-weigh technique on d56 and d112. On d112, steers (n = 64) and non-replacement heifer calves (n = 23) were weaned and placed on a common feedlot diet with individual feed intake monitored using GrowSafe. Feedlot calves were harvested at a commercial facility when ultrasound 12th rib fat thickness (BF) reached 1.2 cm. Initial cow BW and BCS were not different (P > 0.92). At calving, cow BW trended higher (P = 0.08) and BCS was greater (P < 0.01) for COP cows. For COP, trends for increased calf birth BW (P = 0.06) and calves born dead (P = 0.08) coincided with numerically lower unassisted births (P = 0.13). Hay fed cows also tended to be lighter (P = 0.07) at breeding with lower BCS (P = 0.05); nevertheless, overall conception rate was not different (P = 0.83). No differences (P ≥ 0.42) in milk production were detected. Weaning BW, final BW, and days on feed were not different (P ≥ 0.19); and as result, no difference (P = 0.68) in feedlot ADG was detected. Feedlot DMI and G:F were not different (P ≥ 0.48) across treatments. Calf health was monitored with no differences (P ≥ 0.71) in mortality observed. No differences (P ≥ 0.45) were detected for HCW, LMA, BF, marbling score, yield grade, or KPH. No differences (P ≥ 0.32) in quality or yield grade distribution were observed. Prepartum cow diets, differing in energy source and protein type, formulated to be isocaloric and isonitrogenous do not affect performance and carcass traits of subsequent offspring.