Movement Dynamics and Energy Expenditure of Yearling Steers Under Contrasting Grazing Management in Shortgrass Steppe

Abstract

A potential mechanism for lower livestock weight gains with rotational grazing is the additional movement and associated energy expenditures incurred with rotation of animals among paddocks. We evaluated these metrics in 2016 and 2017 using pedometers affixed to free-ranging naïve yearling steers grazing semiarid, shortgrass steppe under contrasting grazing management treatments with the same stocking rate: traditional season-long (mid-May to October) grazing management and collaborative adaptive rangeland management (CARM) at a ranch scale (2-600 ha: ten 130-ha paddocks for each treatment). Mean daily number of steps by steers in paddocks during the grazing season, excluding those associated with moves between paddocks, were 3.0% lower (2016) and 7.8% greater (2017) for CARM, but energy expenditures did not differ significantly between treatments in either year. Daily step counts decreased in traditional rangeland management (TRM) as the grazing season progressed. Step counts decreased from day 1 to day 8 in CARM paddocks following rotation of steers. Steers in the TRM treatment took more steps daily than CARM steers in the first third of the grazing season, but this reversed in the last third of the grazing season. These findings suggest that observed 12%−16% reductions in livestock weight gains with CARM were not influenced by differences in total grazing season steps as energy expenditures of steers did not differ. Two additive influences of within-season steer movement dynamics suggest that forage quality was the primary driver for the decrease in weight gains in CARM. First, fewer steps in the early growing season, when forage quality is highest, indicate reduced selectivity for nutrient-rich patches. Second, more steps by yearlings in the late growing season suggest that these heavier animals expending more energy for maintenance were searching to satisfy gut fill as forage quantity and quality on offer per steer was limiting with the 10-fold higher stocking density.