It is common to graze winter wheat (Triticum aestivum L.) in winter and early spring and to harvest grain in June in the Southern Great Plains. For example, nearly one million hectares of winter wheat were grazed in 2000 in Oklahoma. Cattle grazing in winter or early spring generally yielded greater economic returns compared to the grain-only systems. Management of the dual-purpose wheat is complex because of the complicated interactions and tradeoffs between grain and beef production. In general, more cattle weight gains over longer grazing periods are obtained at the expenses of greater grain yield reduction. A wheat grazing model can be a useful tool for maximizing economic returns of the wheat and beef production systems. The wheat growth module in the Decision Support Systems for Agrotechnology Transfer (DSSAT) model was modified to include an energy-based cattle growth module to simulate dual-purpose winter wheat. The objective of this study is to evaluate and validate the modified model in simulating wheat re-growth and cattle weight gain. Wheat re-growth data from 1992 to 2002 collected at the Chickasha Research Station of the Oklahoma State University (OSU) as well as cattle grazing data including forage availability and animal weight gain during winter and spring grazing collected at Marshal and Stillwater Research Stations of OSU were used to evaluate and validate the model. The preliminary results showed that the model satisfactorily simulated wheat re-growth following clippings. Model performance in predicting cattle weight gain and wheat grain yield will be examined.