Effect of terrain heterogeneity on feeding site selection and livestock movement patterns

Abstract

Feeding site selection is a critical part of livestock foraging that can constrain and/or increase the choices available during diet selection. When livestock choose new feeding sites, vegetation and nutrient profiles can differ from other areas, especially in heterogeneous environments with rugged terrain. Correspondingly, livestock should remain longer in feeding sites in rugged heterogeneous pastures than in homogeneous pastures where animals may alternate among feeding sites to facilitate diet mixing and to prevent satiation. The objective of this study was evaluate how terrain and corresponding heterogeneity may affect the sequence and pattern of feeding site selection of free-roaming livestock. Grazing patterns of mature cows were evaluated on six ranches located in Arizona, Montana and New Mexico. In total, 11–19 cows were tracked for 1–3-month periods at each ranch by using global positioning system (GPS) collars. Positions were recorded at 10- or 15-min intervals and used to identify where cows grazed during the early morning (0500 hours to 1000 hours). Pastures (336–9740 ha) at each ranch were divided into seven to nine sections (48–1082 ha) as an indicator of feeding sites. Classification was based on cattle density and topographical and vegetation types. Sequences of daily section selection were evaluated using transition matrixes. For all ranches, the sequence of section selection differed from what would be expected by chance, indicating that the section selected on the following day depended on the section selected on the previous day. For ranches with relatively gentle terrain, cattle selected different feeding sites ~70% of the tracking period. In contrast, cows at the ranch with the largest pasture and enclosing both mountainous and gentle terrain stayed in the same feeding site for over 10 successive days for 42% of the tracking period. Smaller pastures with only mountainous terrain were intermediate. Cows grazing gentle topography and relatively homogeneous vegetation alternated among feeding sites (sections in the present study) more frequently than cows grazing pastures with more rugged topography and more heterogeneous vegetation. This pattern could help livestock mix forages and select a more diverse diet.