Durunna, O. N., Block, H. C., Iwaasa, A. D., Thompson, L. C., Scott, S. L., Robins, C., Khakbazan, M. and Lardner, H. A. 2014. Impact of calving seasons and feeding systems in western Canada. I. Postweaning growth performance and carcass characteristics of crossbred steers. Can. J. Anim. Sci. 94: 571-582. Crossbred steers (n=272) weaned from early (EC) and late (LC) calving systems (CS) were used to evaluate the impact of two feeding systems (FS) on postweaning performance and carcass characteristics. The steers were randomly assigned to either a rapid-gain feeding (RF) or a slow-gain feeding (SF) system. The RF steers were managed to have body weight (BW) gain of 1 kg d^-1 on a silage-hay diet during the backgrounding period prior to finishing, while the SF steers were first backgrounded on a hay diet (gain of 0.7 kg d^-1), then grazed alfalfa-meadow bromegrass pasture and annual cereal swaths prior to finishing. All treatment groups received a conventional diet during finishing until the steers attained a target backfat thickness or BW or both. There was no difference (P=0.48) between the two FS for the average age of the steers at the beginning of the experiment. There was a CS×FS effect (P<0.01) on the age at slaughter, where the steers in the EC-RF, EC-SF, LC-RF and LC-SF were 426, 659, 504 and 606 d, respectively. The longer time on feed for LC-RF steers compared with EC-RF suggests the potential effect of summer ambient temperatures at finishing. The EC-RF group had the least carcass fat thickness (P<0.01), but there was no main or interaction effect (P>0.08) on dressing percentage or lean meat yield. There was a FS effect (P<0.05) on meat colour and marbling texture where SF steers had more desirable meat colour and marbling texture. Beef producers adopting EC-RF would finish their calves earlier but at a lighter weight.