Cattle Grazing on the Shortgrass Steppe

Cattle are the primary grazers on the shortgrass steppe. For example, during the late 1990s, 21 shortgrass counties in Colorado reported about 2.36 million cattle compared with 283,000 sheep (National Agricultural Statistics Service, USDA, 1997a), 60,000 pronghorn antelope, and a few thousand bison (Hart, 1994). Assuming one bison or five to six sheep or pronghorn consume as much forage as one bovine (Heady and Child, 1994), cattle provide about 97% of the large-herbivore grazing pressure in this region. The ratio of cattle to other grazers is even greater in the remainder of the shortgrass steppe. In 1997, the three panhandle counties of Oklahoma reported 387,000 cattle and only 1300 sheep, whereas the 38 panhandle counties of Texas reported 4.24 million cattle and 14,000 sheep (National Agricultural Statistics Service, USDA, 1997b,c). How ever, only a bout half the cattle in the panhandle counties of Texas and Oklahoma graze on rangeland the remainer are in feedlots. Rangeland research on the shortgrass steppe (Table 17.1 describes the parameters of the major research stations in the shortgrass steppe) has included a long history of both basic ecology and grazing management. The responses of rangeland plant communities to herbivory are addressed by Milchunas et al. (chapter 16, this volume) and to disturbance are discussed by Peters et al. (chapter 6, this volume). Here we focus on research pertaining to three management practices important to cattle ranching on shortgrass steppe: stocking rates, grazing systems, and extending the grazing season via complementary pastures and use of pastures dominated by Atriplex canescens [Pursh] Nutt (fourwing saltbush). Stocking rate, de. ned as the number of animals per unit area for a speci. ed time period, is the primary and most easily controlled variable in the management of cattle grazing. Cattle weight gain responses to stocking rate or grazing pressure (animal days per unit of forage produced) have been quanti. ed in several grazing studies on the shortgrass steppe (Bement, 1969, 1974; Hart and Ashby, 1998; Klipple and Costello, 1960). Average daily gains per animal are better estimated as a function of grazing pressure, rather than stocking rate, as forage production is highly variable in this semiarid environment (Lauenroth and Sala, 1992; Milchunas et al., 1994).