|Bohnert, David - OREGON STATE UNIVERSITY|
Submitted to: Applied Animal Behaviour Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 12, 2008
Publication Date: January 1, 2009
Citation: Ganskopp, D.C., Bohnert, D.W. 2009. Landscape nutritional patterns and cattle distribution in rangeland pastures. Applied Animal Behaviour Science. 116:110-119. Interpretive Summary: The basic causes of uneven cattle distribution and forage utilization on rangelands have not been well studied and are a constantly vexing problem for rangeland managers. We tested the hypothesis that grazing cattle on rangelands seek out the nutritionally superior portions of the landscape and avoid lower quality areas. We first mapped standing crop, fiber content, crude protein content, and forage digestibility in pastures, and then documented the locations grazed and avoided by cattle with global positioning system collars. Cattle preferred portions of pastures with higher than average crude protein and forage digestibility, lower than average neutral detergent fiber, and lower than average standing crop when grazing. Cattle responses to landscape level nutritional dynamics may at least partially explain the seasonal changes in distribution and forage use by cattle across extensive rangeland pastures. These findings should help land and livestock managers understand, explain, and manipulate livestock distribution on their holdings.
Technical Abstract: On rangelands, uneven or unmanaged livestock distribution can adversely affect plant community composition, riparian function, or displace wildlife. These issues have historic precedents and are still a challenge for those managing rangelands. A thorough understanding of the mechanisms governing livestock distribution can help land and livestock managers avoid or ameliorate many deleterious effects. To that end, this research tested the hypothesis that grazing cattle seek nutritionally superior portions of rangeland pastures. Global positioning system (GPS) collars were used to track cattle movement and activity in 800+ ha pastures where the spatial distribution of standing crop, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and forage digestibility (in situ dry matter disappearance (ISDMD)) were mapped in late spring. Four of 5 analyses implied grazing cattle spatially responded to forage quantity/quality attributes. Analyses of variance revealed significant treatment effects for standing crop (P = 0.069), CP (P = 0.006), ISDMD (P= 0.078), and NDF (P = 0.003), but not ADF (P = 0.954). Cattle preferred portions of pastures with higher than average CP and ISDMD, lower than average NDF and standing crop, and were indifferent to ADF. We speculate animal interactions with landscape level nutritional dynamics may at least partially explain the seasonal changes in distribution and forage use by cattle across the landscape. Managed perturbations like mowing, prescribed fire, high intensity grazing, fertilization, and supplementation programs may be used as tools to alter the nutritional status of the landscape and attract stock to historically ungrazed locales. These findings should help land and livestock managers understand, explain, and manipulate livestock distribution on their holdings.