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Delaying calving season from late winter to late spring has been suggested as a way for producers in Wyoming and other high elevation areas of the West to reduce feeding costs. We hypothesized that shifting calving season to a later date would reduce feed costs by providing a closer match between cow nutritional requirements and nutritional quality of grazable forage. The objectives of this study were to estimate the cost of feeding a cow under 5 alternative calving month scenarios (February through June) and to identify alternative lower-cost forage practices that could replace feeding hay. Mixed integer programming models were constructed for each calving scenario with the objective of minimizing the cost of providing energy and protein to a mature cow. Objective function values from each model were compared to identify the low feed cost calving month. The ration was balanced for each month of the year, with requirements dependent on the interaction between the reproductive cycle and environmental conditions. Fat reserves were included as an alternative energy source and body condition was allowed to fluctuate. Under average weather conditions, June was the lowest feed cost calving month with a reduction in annual feed costs of 43 cow-1 over February calving. The cost reduction was a result of a shift from mechanical to stock harvested forage, with the cow being maintained at a lower average body condition during the winter. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020