LAUSR

Grass-fed beef systems (GFB) are one approach proposed to improve the sustainability of animal-sourced foods. Our objective was to estimate carbon (CF) and reactive nitrogen (NF) footprints and cost of production (COP) for northeastern U.S. GFB. A partial life cycle assessment was conducted using the Integrated Farm System Model (IFSM). Systems were characterized using surveys and interviews. Representative operations were simulated in IFSM by grouping farms with similar environments and forage management practices. Environments were defined using USDA Plant Hardiness Zones. Farms were categorized as feed sufficient (FS: produced all supplemental forage on-farm) or feed importing (FI; purchased all supplemental forage). Differences between zones and farm types were analyzed using Dunn’s test with a Bonferroni correction and the Kruskal-Wallis test, respectively. Warmer zones supported longer grazing seasons (P < 0.01), greater pasture legume content (P < 0.05), and denser stocking rates (P < 0.01), resulting in twice the market weight production per hectare compared with farms in cooler zones (P < 0.01). Grazing season length and pasture legume content were similar between farm types (P > 0.1). FI herds were half the size of FS herds (P < 0.01), used 37% more land per animal (P < 0.01), and had 10% lighter market weights with 52% lower market weight production per hectare (P < 0.05). CF, NF, and COP/animal were 1.1, 1.3, and 2.1-fold greater for FI farms, respectively. Zone differences in climate, soils, and pasture legume content affected footprints. In warmer zones where soils had greater clay content, N2O contributed a greater portion of CF and NF, and NO3 leaching was moderate. In the coolest zone with coarser soil, N2O contributed a small portion of CF and NF, with greater NO3 losses. Analyses suggest attention to nitrogen management, efficient resource utilization, and botanical composition might reduce CF and NF.