|Bohnert, David - OREGON STATE UNIV|
Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 2005
Publication Date: March 1, 2006
Citation: Ganskopp, D.C., Bohnert, D. 2006. Do Pasture Scale Nutritional Patterns Affect Cattle Distribution on Rangelands. Journal of Range Management. 59(2):189-196. Interpretive Summary: Uneven cattle distribution on lightly stocked western rangelands often causes portions of a pasture to be heavily grazed while other sections are not grazed at all. Over successive years, ungrazed areas come to support a mixture of weathered vegetation from previous growing seasons and green, current year's herbage. This mixture of old and new growth is often called 'wolfy forage' and it is often wasted by cattle. Our objective was to determine whether grazed and wolfy patches established in pastures in one year affect where cattle will graze the subsequent year. We found cattle foraging in pastures supporting previously grazed and wolfy stands of crested wheatgrass used previously grazed areas 68 percent of the time and wolfy areas 32 percent of the time. During the growing season, cattle removed forage from previously grazed areas while plant growth in wolfy patches actually increased herbage accumulations. Cattle will eventually forage in wolfy areas, but only after exhausting herbage supplies in the previously grazed sections. This study determined that uneven forage utilization patterns established in one year are self sustaining, and they will dictate where cattle will forage in large pastures in subsequent years. To obtain more uniform use of herbage in pastures and reduce levels of waste, wolfy forage can be removed with prescribed burns, mowing, or heavy grazing applied when grasses are not growing and cattle graze less selectively. Cattle will be more willing to graze over a larger area and less forage will be wasted in subsequent years. This research will benefit cattle ranchers and land managers.
Technical Abstract: Heterogeneous distribution patterns of various ungulates about the landscape have long interested ecologists, and can be a particularly vexing problem for resource managers. While livestock preferences for leaves over stems among plants and patches of herbage are well documented, the effect of wolfy forage (herbage supporting both green and cured materials) on beef cattle distribution and nutrition at landscape scales has not been investigated. The primary objective of this research was to determine the relative proportions of time cattle spent foraging within wolfy and conditioned (areas supporting only current seasons growth) portions of pastures. Other objectives included: comparing distances traveled by foraging cattle in conditioned and wolfy sectors; determining diet quality of cattle confined to wolfy and conditioned sections of pastures; and quantifying levels of forage utilization by cattle in wolfy and conditioned treatments. These were accomplished in a randomized complete block study with GPS collars used to monitor cattle movement and activity in treated crested wheatgrass (Agropyron desertorum (Fisher ex Link) Schultes) pastures. Over a y-day trial, cattle were detected in wolfy and conditioned areas 41 and 59% of the time, respectively. When cattle were grazing, 32% of observations were in wolfy sectors, and 68% occurred in conditioned areas. With a decline in standing crop in the conditioned treatment, cattle switched to wolfy herbage (73% of observations) on the seventh day of the trial. Standing crop was reduced by 13 to 40% in the conditioned treatment and increased by almost 10% in wolfy portions of the pastures. Despite disparities in crude protein levels of standing crop in wolfy (mean=6.5%) and conditioned (mean=11.3%) treatments, cattle confined to treatments harvested diets of similar quality (mean=13.6% CP). Cattle walked further when making transitions between treatments, and walked further each day as the trial progressed. A preference of foraging cattle for portions of pastures that were grazed during the previous growing season suggests that utilization patterns established by livestock at landscape scales are self sustaining.