• Seasonal preferences of steers for prominent northern Great Basin grasses

      Cruz, R.; Ganskopp, D. (Society for Range Management, 1998-09-01)
      The objective of this research was to determine, on a seasonal basis, the relative preferences of cattle for 7 native grasses and d crested wheatgrass (Agropyron desertorum (Fischer ex Link)Schultes), a long-used introduction in the Pacific Northwest. Methods involved observing forage selection processes of 3 steers in paddocks, where plants existed in equal densities and in rangeland pastures with variable forage composition. Design of paddock and pasture studies was a randomized-complete-block with 3 replications, 3 stages of phenology (vegetative, anthesis, and quiescent), and 8-11 forages. Dietary proportions as indexed by bite-counts changed (P < 0.01) with phenology and varied among species. Diets were more similar (P < 0.05) than forage composition between the 2 study areas (paddocks and native pastures), and became less similar (p < 0.05) as phenology of the grasses advanced from vegetative growth through anthesis and quiescence. Steers were selective grazers during vegetative and anthesis stages of phenology, and despite variations in herbage availability, 'Nordan' crested wheatgrass was the most prominent dietary component in paddocks and pastures. Variation in proportions of grasses in the diet was associated (P < 0.05) with measures of available forage in the paddocks (r = 0.46-0.89, average = 0.72) but poorly associated with herbage composition in pastures (r = 0.41-0.02, average = 0.12). Inconsistencies in rankings of relative preference indices and dietary proportions of grasses suggested that measures of herbage availability may confound the predictive utility of relative preference indices. More grasses were acceptable to cattle at quiescence, with crested wheatgrass ranging from 8-26% of the diet. We suggest that with proper management, interseedings of crested wheatgrass on native range may be used to lessen grazing demands previously borne by native perennials early in the grazing season.
    • Variations in nutritional quality and biomass production of semiarid grasslands

      Corona, M. E. P.; de Aldana, B. R. V.; Criado, B. G.; Ciudad, A. G. (Society for Range Management, 1998-09-01)
      The effect of the growing season and topographic zone on biomass production, protein content, cell content (CC), lignin, cellulose, hemicellulose, digestibility (DMD), and mineral element concentrations (P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn) were studied in herbage samples collected from semiarid grasslands in Central Western Spain. Protein and mineral contents decreased as the growing season progressed whereas fibre properties tended to increase. Topographic gradient significantly affected peak biomass production, fibre properties, protein and mineral contents. Stepwise multiple regression showed that the prediction of biomass production on these areas was related to cellulose, Na, Fe, and Mg contents in the grassland community whereas fibre properties were mainly predicted by Ca, Na, and Cu. Principal component analysis indicated that the temporal evolution (component II) of the organic variables determined pasture quality whereas most of the variation in mineral content was related to the topographical gradient (component I). Some organic and inorganic parameters may cause deficiencies in cattle grazing en the upper and middle zones, mostly at the end of the growing season. The data suggest that information about the temporal and spatial variations of the production and nutritional quality of semiarid grassland is necessary for making correct management.