Beef production in the northern Great Plains and similar semi-arid environments depends on raising young beef females that can adapt to intra and interannual changes in forages and nutritional quality that accompanies these changes. The objective of the study was to determine the effect of rumen protected methionine and calcium propionate supplements fed to nulliparous beef cows on body weight, calf performance, and milk production. Four isocaloric and isonitrogenous supplements were formulated and fed at a rate of 908 g center dot cow- 1 center dot d- 1 for 101 d (Yr 1) and 127 d (Yr 2). Supplements contained 183 g CP and approx. 560 g TDN: 1) control (Con); 2) rumen protected methionine (Met; inclusion of 20 g center dot hd- 1 center dot d- 1 Mepron85); 3) calcium propionate (Prop; inclusion of 50 g center dot hd- 1 center dot d- 1 NutroCal (R)); 4) or rumen protected methionine and calcium propionate (Met & thorn;Prop; inclusion of 20 g center dot hd- 1 center dot d- 1 Mepron85 (R), and 50 g center dot hd- 1 center dot d- 1 NutroCal (R)). Cows from each supplement treatment were randomly assigned to pastures targeting one of two stocking rates to achieve either 40 % (moderate) or 60 % (heavy) utilization for two consecutive years. Nulliparous cows' body weight at the termination of the supplementation period were similar (P = 0.99) for supplemental treatment, however cows in the moderate stocking rate pastures tended to be heavier (P = 0.06). A supplement x year interaction was measured for calf birth weight (P = 0.04) with no influence derived from pasture stocking rates on calf birth weight (P = 0.36). Calves born from cows that received the Met supplement were heavier in Yr 2 whereas calves in the Met+Prop treatment were heaviest in Yr 1 with all other treatment x year combinations being similar. A supplement x year effect was observed for peak milk production and energy corrected milk (ECM, P = 0.01 and P = 0.03, respectively). Peak milk yield was 3.8 kg center dot d- 1 lower for Con when compared to the Prop cows and ECM was 3.9 kg center dot d- 1 lower for Con when also compared to the Prop cows in Yr 2 of the study, whereas all other treatment combinations within and across the two years were similar. These data indicate that rumen protected methionine and calcium propionate can augment dietary efficiencies and magnitude of responses are dependent on environment.