Grazing Behavioral Responses of Beef Cattle to Medusahead Invasion

Despite thorough documentation of the ecological impacts of medusahead (e.g., Davies and Svejcar 2008) and challenges associated with control and restoration of medusahead-invaded rangeland (Davies and Johnson 2008), little is known about the effects of invasion to cattle grazing behavior. Much anecdotal evidence exists suggesting medusahead is palatable to grazing livestock only briefly in early spring prior to development of a seed head. However, no studies have sought to document the grazing preferences and behavior of beef cattle on medusahead-invaded rangeland in relation to seasonal changes in forage quality/ palatability of medusahead relative to desirable rangeland vegetation. In addition, little information is available for informing decisions about appropriate grazing management strategies for beef cattle on medusahead-infested rangeland.

Objectives

The objectives of this study are to determine: 1) seasonal forage quality of medusahead-invaded rangeland relative to adjacent rangeland supporting desirable vegetation; 2) relative grazing preference of beef cattle for medusahead-invaded rangeland and adjacent rangeland supporting desirable vegetation; 3) seasonal cattle behavioral responses to medusahead invasion.

Study Area

The study is being conducted on the Burns District BLM Stinkingwater and Riddle Mountain Allotments near Drewsey and Happy Valley, OR, respectively.

Methods

• All areas (patches) principally comprised of medusahead are being identified and mapped in each study field.
• Concurrently, areas of predominantly desirable rangeland vegetation (primarily crested wheatgrass) are being identified and mapped.
• The study is employing global positioning system (GPS) collars to measure seasonal (April through August) behavioral responses of beef cattle to medusahead invasion.
• Concurrent with collection of cattle behavioral information, composite forage quality samples are being gathered on a biwieekly schedule during the study.
• Forage samples are being analyzed for crude protein (CP) and total digestible nutrients (TDN) content to determine relative seasonal variation in forage quality of medusahead and desirable rangeland vegetation.
• Preliminary results from one pasture for the first year of the study are presented below. Unfortunately, the sampling period was cut short due to the livestock producer’s need to move cattle from the study field in response to a diminishing forage supply prior to the end of the grazing season.

Preliminary Results (Year 1 cattle behavior and forage quality results)

• Grazing preference of beef cattle for crested wheatgrass and medusahead varied throughout the season.
• Cattle generally expressed a strong preference for grazing crested wheatgrass dominated plant communities late April through mid-June.
• CP content of crested wheatgrass was approximately 1 to 3% higher than medusahead from early May through the end of June, at which time CP content of crested wheatgrass declined to below that of medusahead.
• TDN concentrations of crested wheatgrass were 3 to 4.5% higher than medusahead in May, whereas TDN was not different between the forages in June.

Discussion

• Preliminary results from the first year of the study suggest important differences exist in nutritional quality between crested wheatgrass and medusahead during the growing season that may contribute to beef cattle grazing behavior in rangelands invaded by medusahead.
• Cattle largely avoid grazing in patches of medusahead when their nutritional quality is substantially less than that of surrounding vegetation, which was the case throughout the majority of the growing season during the first year of the study.

Literature Cited

Davies, K. and T. Svejcar. 2008. Range Ecology & Manage. 61:623-629.

Davies, K. and D. Johnson. 2008. Rangelands 30:13-15.