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Nutritional challenges placed upon the lactating cow can be extreme in Arizona. One challenge placed upon the cow is the extra nutritional requirements caused by lactation. Figure 1 illustrates the weight loss which usually occurs in a lactating cow during the first 45 to 60 days of lactation. At the period of time at which the cow has lost the most weight, producers are trying to rebreed her in order to maintain a yearly calving interval. It is usually not possible to entirely prevent weight loss during early lactation with range cattle. A better strategy is to plan ahead to allow for weight loss by building or maintaining body fat stores before calving. Another challenge with Arizona ranching operations is the reduction in forage quality with mature forage. Rainfall often occurs in a biannual pattern and forage quality before the monsoon rains and in late winter can be low. As forage matures, protein, total digestible nutrients (TDN), and phosphorus often decline below levels considered adequate. In addition, certain trace minerals may be deficient year round. It is a good practice to analyze dormant forage to determine protein, TDN, and phosphorus content. You can then match cowherd supplementation to the forage resource (Sprinkle, 1996a). It is also a good practice to analyze forage for trace mineral status over two or three years to establish baseline data for your ranch. Trace minerals in Arizona which may be of concern are selenium, copper, zinc, sulfur, and molybdenum. There are several options one can take to help meet the nutritional challenges placed upon cows by lactation and the environment.