Historically, the objective of supplementation programs for grazing cattle has been to address nutrient deficiencies based on the difference between animal nutrient requirements and the nutrients provided by the forage, with emphasis on improving forage utilization and animal performance. However, growing natural resource and land management challenges and expectations have resulted in another reason to use a supplementation program: modification of grazing behavior.
Consequently, strategic supplementation is a tool that has been used to attract cattle to underutilized locations within a pasture, minimize the time spent in and/or utilizing riparian areas, modify grazing time and harvest efficiency, and potentially lessen the severity of wildfires by reducing fine fuels on the landscape. This is important because when cattle graze large, extensive pastures, specifically arid and semiarid rangelands with rough topography, they tend to prefer areas with gentle terrain and proximity to water while avoiding those areas more distant from water and with steeper slopes. This can concentrate grazing in certain locations, year after year, resulting in localized overgrazing while significant portions of the pasture are rarely visited and have abundant forage.
Related, a primary challenge facing managers of grazing lands – especially those in the western U.S. where almost 250 million acres of Bureau of Land Management and U.S. Forest Service lands are grazed – is the development of grazing systems that are economically viable while maintaining or improving the ecological function and multiple-use requirements of the land resource. Strategic supplementation can help address this challenge; however, in order to effectively design a supplementation program that modifies grazing behavior, managers need to understand the abiotic and biotic factors that affect grazing behavior and distribution, which in large, extensive pastures with rough topography includes differences in forage quality and quantity across the landscape, seasonality of grazing preferences, watering locations, thermal cover, terrain heterogeneity, fire history and animal trails. A knowledge and understanding of these factors and their interactions is critical for the implementation and success of a supplementation program. If managed appropriately, this type of supplementation strategy can help maintain or improve landscape ecological function by decreasing areas with excessive utilization and improving use of underutilized areas, thereby improving grazing distribution and reducing the potential negative impacts of overgrazing, thereby benefiting livestock production, wildlife habitat and numerous other ecosystem services.
Supplementation of salt and/or mineral away from water locations is often a strategy used to encourage better livestock distribution; however, results are mixed on its ability to actually improve livestock distribution. In contrast, protein supplements are an effective method for manipulating livestock grazing distribution in large, topographically diverse pastures common to the western U.S. This is because they provide a highly palatable, nutritional incentive for cattle to travel to areas of pastures that are farther from water, on steeper slopes, have less palatable vegetation or are at higher elevations.
Strategic placement of protein supplements can reduce grazing pressure on sensitive and preferred areas (e.g., riparian) of pastures. Furthermore, cattle have been shown to utilize dormant forage in the late fall in areas surrounding strategically placed protein supplements at distances up to 2.5 miles from water, thereby decreasing forage biomass and reducing the risk of wildfire. Also, strategic placement of protein supplements has, through improved grazing distribution, increased the length of the grazing season by improving grazing efficiency and increasing forage intake by cattle on underutilized areas, thereby helping reduce total yearly feed costs.
Though research has demonstrated that providing nutritional supplements can alter cattle grazing distribution, knowledge of the relationship and interaction that landscape attributes have on supplement use by cattle in pastures containing riparian areas common to the rugged coniferous forests of the western U.S. is extremely limited or not available. Consequently, during a multiyear grazing study in a forested grazing allotment with critical salmon and steelhead habitat (Starkey Experimental Forest and Range, Wallowa-Whitman National Forest), researchers with Oregon State University and the Pacific Northwest Forest Research Station in northeastern Oregon evaluated the disappearance of protein supplement in the uplands by cow-calf pairs as it related to season (late versus early) and landscape attributes around each supplement site (including slope, distance to upland water sites and to the riparian area, canopy cover and aspect). They found the best predictor of protein supplement use was a model that included slope, canopy cover and distance to supplemental water. In addition, supplement disappearance was over 60% greater late in the season (after Aug. 15) compared with earlier in the grazing season (Figure 1).
In conjunction with information on pasture access and road and trail networks, ongoing research is using the data obtained to develop decision support tools to help identify strategic supplement locations that will provide the best opportunity to alter cattle grazing distribution to address natural resource and livestock management objectives (Figure 2).
Supplementation to address nutrient deficiencies will always be an important aspect of the livestock production enterprise; however, because rangelands are increasingly valued for many features and services other than just providing forage for livestock and wildlife, the ability of livestock producers to remain competitive when utilizing extensive landscapes will also depend on the development of management practices – such as strategic supplementation – that use ecologically based principles of land management.
