Adaptive multi-paddock grazing management reduces diet quality of yearling cattle in shortgrass steppe

Abstract

Adaptive multi-paddock (AMP) grazing is hypothesised to improve livestock diet quality by allowing managers to move livestock among paddocks in a manner that tracks phenological variation in forage growth related to variation in plant community composition. We compared yearling steer (Bos taurus) dietary crude protein (CP), digestible organic matter (DOM), and diet composition on a ranch-scale (2600 ha, 10 pairs of 130 ha paddocks) experiment in shortgrass steppe for 6 years (2014–2019) in contrasting grazing treatments: Collaborative Adaptive Rangeland Management (CARM, a type of AMP with a stakeholder group making science-informed management decisions within the grazing season) and season-long, continuous grazing (TRM, traditional rangeland management). These grazing treatments had the same system-level stocking rate annually but differed in stocking density, with CARM being 10-fold higher than TRM because of all steers in the CARM treatment being in a single herd. Mean grazing-season dietary CP was consistently 13–28% higher in TRM than CARM; in contrast, DOM in TRM was similar to CARM or only slightly higher (2.5%). Differences in diet quality between CARM and TRM grazing strategies were largest early in the grazing season, with CP being 14–36% higher for TRM compared to CARM steers during the first 4 weeks; these diet-quality differences between treatments disappeared towards the end of the grazing season. Implementing AMP on the basis of a diverse stakeholder group’s experiential knowledge about plant communities, soils, and ecological sites did alter within-grazing season plant functional group contributions to steer diets. Although we implemented adaptive decision-making within the grazing season, which allowed CARM steers to track the seasonal phenology of C₃ versus C₄ grasses as steers rotated among paddocks varying in plant community composition, these adaptive movements did not offset the detrimental effects on diet quality associated with grazing in a herd with 10-fold higher stocking density. Managers applying AMP in semiarid rangelands should be cognisant that high stocking density can be associated with lower diet quality early in the growing season, which can compromise livestock gain responses.