Adaptive, multi-paddock, rotational grazing management alters foraging behavior and spatial grazing distribution of free-ranging cattle

Authors: Augustine, David; Kearney, Sean; Raynor, Edward; Porensky, Lauren; Derner, Justin

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2023
Publication Date: 4/13/2023
Citation: Augustine, D.J., Kearney, S.P., Raynor, E.J., Porensky, L.M., Derner, J.D. 2023. Adaptive, multi-paddock, rotational grazing management alters foraging behavior and spatial grazing distribution of free-ranging cattle. Agriculture, Ecosystems and Environment. 352. Article 108521. https://doi.org/10.1016/j.agee.2023.108521.
DOI: https://doi.org/10.1016/j.agee.2023.108521

Interpretive Summary: Although ranchers often rotate livestock through multiple pastures during the growing season, there is still considerable uncertainty in how such rotations affect the behavior and distribution of the livestock while they occupy a given pasture, or how grazing patterns might differ if livestock grazed the same area at lower density over a longer time period. We examined this question on semi-arid, shortgrass rangeland in Colorado using an experiment that compared a single large herd rotated adaptively among 10 pastures during the growing season versus 10 small herds, each of which occupied their own pasture for the entire growing season. Previously, we reported that the adaptively rotated cattle gained 14% less weight than cattle grazing pastures season-long. In this paper, we analyze data collected by GPS tracking devices placed on a subsample of the cattle in both management regimes, to evaluate effects on the foraging behavior and grazing distribution of the cattle. We found that rotational cattle (large herd at high stock density) grazed in more linear pathways and at a slower step rate compared to season-long cattle (small herds at low stock density). At high stock density cattle also grazed continuously for longer bouts each day. These differences in foraging behavior indicate that at high stock density, cattle consume lower quality forage because they are constrained to selecting bites from available forage directly in their line of travel, and do not employ foraging tactics that help them find high-quality bites or patches of high-quality plants. Rotational grazing management resulted in substantially more even distribution of grazing across the pastures in wet years, but had minimal effect on grazing distribution in dry years when forage was in limited supply. Our results help explain how rotational grazing management can reduce the amount of weight that cattle gain in the growing season, while having little effect on vegetation productivity.

Technical Abstract: Background: Sustainable management of grazinglands depends upon understanding how management practices influence grazing livestock movements in space and time. We conducted a ranch-scale (2,600-ha) social-ecological experiment to examine how movement ecology of cattle differs between a single large herd rotated adaptively among paddocks (collaborative, adaptive rangeland management; CARM) versus continuous, season-long grazing of paddocks by small non-rotational herds (traditional rangeland management; TRM). We analyzed how differences in movement patterns between the two treatments may be linked to reductions in cattle growth rates and diet quality in the CARM treatment, relative to TRM. Results: Cattle in the CARM treatment exhibited more linear grazing pathways, moved at lower velocity while grazing, and exhibited longer grazing bouts early in the growing season compared to TRM cattle. Grazing time within any given 10 x 10 m area was distributed more unevenly across TRM vs. CARM paddocks in years with average or above-average precipitation, but not in dry years. In all years, areas of high and low grazing intensity were more spatially clustered in TRM than CARM paddocks. Conclusions: To inform the global debate around animal movement-focused grazing strategies, we provide insights into movement ecology of cattle in semiarid grazinglands. Movement patterns of cattle managed using adaptive, multi-paddock rotations at high stock density (CARM) are consistent with less selective foraging. Such cattle move more slowly and in more linear pathways, and graze continuously over longer time intervals, thus forming a “grazing front” that moves across the paddock and distributes grazing pressure in a more spatially homogeneous fashion. In years with substantial forage production, TRM cattle spent more time than CARM cattle in preferred areas of the paddock and foraged in more circular patches. In dry years, however, both treatments resulted in similarly even grazing distribution, likely due to limited intra-paddock variation in forage quality and quantity. At the ranch scale, these different intra-paddock movement patterns led to reductions in animal performance and no overall effect of grazing management on forage production.