Nitrogen (N) intake and output were measured on free-ranging cattle throughout the grazing season to determine how ingested N was cycled back into the system. Only 16% of the nitrogen that was ingested over the grazing season was used for growth while the rest was cycled back into the system as urine and feces. Dry matter intake and fecal output were lower and N intake was greater when digestibility of plant materials was high. Urinary N outputs were related to forage N and digestibility, while fecal N output was more related to dry matter intake. Metabolizable energy and crude protein intake were above maintenance requirements during the growing season, but were inadequate during the dormant season. Results suggest that energy and crude protein intake limited cattle production on shortgrass steppe range, but the identity of the limiting nutrient changed seasonally. The authors conclude that because maintenance levels are specific to classes of livestock, patterns of nutrient limitation may differ for other classes such as mature or lactating cows.
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