Steer Growth Performance and Enteric Gas Flux Across Backgrounding Phases in the Western Great Plains

This study assessed the changes in growth performance and enteric gas flux of stocker steers across the postweaning phase and stocker phase of the production system in the western Great Plains. The objectives were to (1) evaluate growth performance and gas flux of steers originating from different production environments (e.g., diet and management) in the two phases of backgrounding, and (2) compare automated head-chamber system (AHCS)-measured enteric methane (CH_4, g CH₄ d⁻¹) emissions to predictions using Intergovernmental Panel on Climate Change (IPCC) Tier 2 methodology. In the winter postweaning phase, one group was stocked on shortgrass rangeland, and two groups were managed in drylot before all three groups were collectively stocked on summer rangeland. Steers winter-stocked on Colorado rangeland (hereafter, Colorado-grazing steers) doubled their average daily gain (ADG, kg steer⁻¹ day⁻¹) during the summer stocker phase on extensive rangeland. Conversely, steers that spent the winter postweaning phase in drylot in Nebraska (hereafter, Nebraska-drylot steers) or Colorado (hereafter, Colorado-drylot steers) had the same or reduced ADG in the stocker phase compared with the postweaning phase. Colorado-grazing steers produced 58% more CH₄ in the stocker phase than in the postweaning phase, whereas Nebraska-drylot steers emitted 11% lower CH₄ in the stocker phase than in the postweaning phase. Methane production was similar between phases for Colorado-drylot steers. Concomitantly, CH₄ intensity (g CH₄ kg⁻¹ ADG⁻¹) decreased for Colorado-grazing and Nebraska-drylot steers, whereas no difference was detected for Colorado-drylot steers between phases. A comparison of measured enteric CH₄ emissions to IPCC predictions for the same animal class and diet in each production phase revealed that predictions for five of six animal-phase combinations diverged from AHCS-measured CH₄ production. This longitudinal experiment suggests that accounting for the variation in gas flux across each phase in growing steers may inform assessments of the sustainability of beef cattle related to greenhouse gas mitigation strategies.