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Botanical composition of horse and cattle diets from fecal anaiysis and nutrient quality of hand-harvested forages used by these herbivores were evaluated to assess dietary quality during the summer and winter seasons of 1981 in the Wyoming Red Desert. Dietary crude protein estimates averaged 7.5fO.l% and 9.M0.5% during the summer for horses and cattle, respectively. Dietary crude protein estimates in the winter were lower, averaging 6.1&O% and 6.ofO% for horses and cattle, respectively. Estimated dietary calcium levels for both herbivores were high through the summer and winter, while dietary phosphorus levels appear to be deficient during both seasons. Average in vitro dry matter disappearance coefficients for horses and cattle during the summer were 52f2%,and 52f2%, respectively. During the winter these values dropped to 39x0% and 4ofl% for horses and cattle, respectively. Estimates of the nutrient content of diets selected by animals from a vegetation complex are useful for evaluating the nutrient quality of a habitat for ungulates. For free-ranging ungulates like feral horses (Equus cuballus) and cattle (Bos tuurus), gross estimates must sometimes be substituted for more refined techniques when the latter are limited. Information of the latter type is not available for this region for these 2 species. The objective of this study was to evaluate nutrient content of diets for horses and cattle grazing together under a heavy and a moderate stocking level using botanical composition of diets determined by fecal analyses, and nutrient composition of herbages determined from hand-harvested samples. Study Area and Methods The study was conducted in the Red Desert of Wyoming approximately 93km northeast of Rock Springs, Wyo., in Sweetwater County. A semi-arid climatic pattern prevails over the area. Three distinct vegetation types-sagebrush-grass, saltbush, and greasewood-rabbitbrush-cover most of the area. For a more complete description of the study area see Krysl et al. (1984). Grazing treatments used were: moderate grazing intensity of horses and cattle in combination (MHC) and heavy grazing intensity of both species in combination (HHC). Summer grazing period was from June 7 to August 7, 1981, while winter grazing period was from November 7 to December 21, 1981. Detailed information on grazing treatments is found in Krysl et al. (1984). Composite samples of 29 ungrazed forage species were obtained at approximately 14-day intervals through the summer study period by hand-harvesting 20 or more plants of each species from the general area. Only 12 forage species were collected during the winter period due to decreased availability. Specific plant parts were selected to simulate those observed being consumed by horses Authors, lirst five? at the time of the study, were research technicians, Division of Animal Science; aswtant professor, Division of Range Management; and associate professor, Division of Animal Science, University of Wyoming, Laramie 82071. Mr. Krysl is currently graduate assistant, Department of Animal and Range Sciences, Box 3-1, New Mexico State University, Las Cruces. The study was supported by funds from the Bureau of Land Management under contract AA851-CTO-31. The authors thank Pat Fazio for helping in the laboratory analysis. Reviews of the manuscript by Drs. F.C. Hinds, F.E. Busby, and J.L. Holechek were very helpful and we appreciate their efforts. Manuscript received June 11, 1982. 252 and cattle. Although studies indicate hand-picked samples sometimes differ in nutrient content from samples collected with an esophageally fistulated animal (Edlefsen et al. 1960, Campbell et al. 1968) the magnitude of the difference is not great enough to eliminate the method for use in range nutrition studies. Samples were weighed and frozen at approximately -YC in a conventional freezer in the field. They were later dried in a forced-air oven at 45°C for 48 hours, reweighed for dry matter determination, ground in a Wiley mill to pass a 40-mesh screen, and stored in air-tight containers for chemical analysis. Forages were analyzed for percentage nitrogen by the Kjeldahl procedure [Association of Official Agricultural Chemists (AOAC) 19701 and converted to percentage crude protein using (%N X 6.25). In vitro dry matter disappearance (IVDMD) was determined by an acid-pepsin modification (Vavra et al. 1973) of the method described by Tilley and Terry (1963). Calcium and phosphorus concentrations were determined for hand-harvested samples as described by AOAC (1970). Since nutrient intake could not be measured directly, a weighted nutrient consumption estimate was obtained for each collection period on both study areas in a manner similar to Urness and McCulloch (1973). Estimates of dietary crude protein, IVDMD, calcium, and phosphorus for horses and cattle were determined by multiplying the nutrient content of each collected plant species by that species percentage relative frequency in the diet (Krysl et al. 1984). These weighted values were then summed across all plant species within each season and divided by the percentage of the diet tested to estimate the nutrient content of the diet. Results and Discussion Summer Indian ricegrass (Oryzopsis hymenoides), prairie Junegrass (Koeleria cristata). thickspike wheatgrass (Agropyron dasystachyum), needleleaf sedge (Carex eleocharis), Sandberg bluegrass (Pea sandbergii), bottlebrush squirreltail (Sitanion hystrix), and needleandthread (Stipa comatu) were the major grasses and sedges consumed by horses and cattle. Important shrubs utilized by horses and cattle were winterfat (Ceratoides lanata), fourwing saltbush (Atriplex canescens), spiny hopsage (Grayia spinosa), and nuttall saltbush (Atriplex nuttulli) (Krysl et al. 1984). Grasses and sedges exhibited the lowest crude protein levels followed by forbs and shrubs during the summer (Table 1). Troelsen (1969) has reported forbs are generally more nutritious than grasses with grasses generally showing sharp declines in nutrients with advancing season. Dietary crude protein estimates for cattle in the HHC pasture averaged 8.5% and ranged from 9.9% in early summer to 6.8% by summers end, while estimates for the MHC pasture were slightly higher (9.5%) for the same time period, ranging from 10.7 to 8.2%, (Table 2). The slight difference between pastures was the result of cattle in the MHC pasture utilizing substantially more shrubs (36% vs 28%) and forbs (16% vs 9%) than cattle in the HHC pasture (Krysl et al. 1984). Shrubs during this time generally contained higher crude protein levels than grasses and sedges (Table 1). JOURNAL OF RANGE MANAGEMENT 37(3), May 1994 Table 1. Percent crude protein (CP), calcium (Cr), phosphorus (P), and in vitro dry matter disappearance (IVDMD) f standard deviation for major summer forages in 1981 on the study area.

Horses and Cattle Grazing in the Wyoming Red Desert, II. Dietary Quality