Spring calving (Block 1; n = 70 heifers; BW 208 ± 21.7 kg; age 231 ± 17.0 d) and fall calving (Block 2; n = 72 heifers; BW 225 ± 31.7 kg; age 276 ± 12.8 d) heifers were used to test the effects of feeding 20 mg of bambermycin (Gainpro; Huvepharma; Sofia, Bulgaria) or 150 mg of monensin (Rumensin; Elanco Animal Health, Greenfield, IN) in 0.91 kg/d corn gluten feed based supplements compared with non-medicated (Control) supplements on growth performance and development of grazing heifers. Heifers were allocated by breed, BW, and age to pasture groups (n = 5/group for Block 1 and n = 6/group for Block 2). Pasture groups were then randomly assigned to treatment (Control n = 4 pastures in Blocks 1 and 2; bambermycin and monensin n = 5 pastures in Block 1 and n = 4 pastures in Block 2). Block 1 began on 29 October 2013 and lasted 189-d, and Block 2 began on 24 June 2014 and lasted for 161-d. Heifers were weighed full on 2 consecutive days at beginning and end of each block. Reproductive tract scores (1 to 5 score) were assessed before breeding using ultrasound in Block 1 and rectal palpation in Block 2. In Block 1, heifers grazed non-toxic endophyte infected tall fescue pastures, while in Block 2 heifers grazed bermudagrass pastures until 14 October and then grazed non-toxic endophyte infected tall fescue pastures. Heifers were AI bred over 10-d, and natural service bulls were placed with heifers 14-d following final AI date. Data were analyzed as a randomized complete block design using the mixed procedure of SAS (SAS Inst. Inc., Cary, NC) least squares means were separated using contrasts: Control vs. Medicated and bambermycin vs. monensin. Ending BW and ADG of Control (323 ± 4.8 kg and 0.68 ± 0.0167 kg/d) was less (P ≤ 0.04) than medicated, yet monensin (346 ± 4.6 kg and 0.73 ± 0.0163 kg/d) and bambermycin (344 ± 4.6 kg and 0.74 ± 0.0163 kg/d) did not differ (P ≥ 0.69). Reproductive tract scores (3.5 ± 0.60), AI pregnancy rates (30 ± 12.3%) and total pregnancy rates (82 ± 11.5%, respectively) did not differ (P ≥ 0.36) among treatments. This experiment indicates that both bambermycin and monensin effectively increase performance of growing heifers, but did not affect reproduction.