Relative costs and feeding strategies associated with winter/spring calving

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 Wes t to reduce feeding costs, We hypothesized that shifting calving season to a later date would reduce feed costs by providing a closer match between co w 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 identif y alternative lower-cost forage practices that could replace feeding hay. M ixed integer programming models were constructed for each calving scenario with the objective of minimizing the cost of providing energy and protein t o 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 t he reproductive cycle and environmental conditions. Fat reserves were inclu ded as an alternative energy source and body condition was allowed to fluct uate, Under average weather conditions, June was the lowest feed cost calvi ng 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 sto ck harvested forage, with the cow being maintained at a lower average body condition during the winter.