• Dietary Relationships Among Feral Horses, Cattle, and Pronghorn in Southeastern Oregon

      McInnis, M. L.; Vavra, M. (Society for Range Management, 1987-01-01)
      Management of sympatric ungulates on multiple use lands requires knowledge of how species exploit resources available to them. We examined seasonal food habits, dietary overlap, and dietary quality of sympatric feral horses (Equus caballus), cattle (Bos taurus),, and pronghorn (Antilocapra americana) in south-eastern Oregon from May 1979 through March 1981. Seasonal diets of each ungulate species were determined by microhistological analysis of feces. At least 88% of the mean annual diets of horses and cattle consisted of grasses. Principal species consumed by these ungulates were bottlebrush squirreltail (Sitanion hystrix (Nutt.) J.G.Smith), bearded bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith), and Thurber needlegrass (Stipa thurberiana Piper). Because dietary overlap between horses and cattle was high each season (62-78%), we concluded a strong potential existed for exploitative competition under conditions of limited forage availability. Pronghorn diets consisted largely of woody sagebrush (Artemisia) species in fall and winter, and a mixture of forbs in spring and summer. Dietary overlap between horses and pronghorn varied from 7% (summer) to 26% (winter). Overlap between cattle and pronghorn varied from 8% (winter) to 25% (spring). These lower levels of overlap indicate a wider buffer between noncompetitive coexistence and exploitative competition. Pronghorn generally selected diets containing higher levels of crude protein (CP) and lower levels of acid-detergent fiber (ADF) than horses or cattle. We observed few differences in seasonal dietary quality between horses and cattle.
    • Grazing System Influences on Cattle Performance on Mountain Range

      Holechek, J. L.; Berry, T. J.; Vavra, M. (Society for Range Management, 1987-01-01)
      A 5-year study was conducted to evaluate the influences of rest-rotation, deferred-rotation, and season-long grazing systems on cattle diet botanical composition and quality and weight gains on mountain rangeland in northeastern Oregon. The grazing season in each year lasted from 20 June to 10 October. Esophageally fistulated animals were used to evaluate diet quality and botanical composition. All study pastures included forest, grassland, and meadow vegetation types. Each pasture had a north and southfacing slope divided by a riparian zone and creek. The grazing pressure for each system was similar. Grazing intensity was the same as National Forest Allotments in the area. There were no differences (P>.05) in weight gains among the 3 systems when data were pooled across years. Crude protein, in vitro organic matter digestibility, and acid detergent fiber percentages in fistula samples did not differ (P>.05) among systems for any year of study or for data pooled across years. Mid-season movements of cattle under the rest-rotation system had little influence on their diet and performance compared with cattle under the season-long system. Key forages in cattle diets were Idaho fescue (Festuca idahoensis), bluebunch wheatgrass (Agropyron spicatum), and common snowberry (Symphoricarpos albus). Cattle diet botanical composition under the 3 grazing systems did not differ (P>.05).