338. Farm-level Implementation of Climate-Smart Strategies to Reduce Enteric Methane in Grazing Beef Cattle–An Exploratory Case Study.

Abstract Cow-calf operations represent a major agricultural activity in South Carolina, based on Tall fescue (Schedonorus arundinaceus) pastures. Beef operations contribute 60–70% of methane (CH4) emissions in U.S. systems. Climate-smart practices including rotational grazing, organic fertilization, and legume overseeding have been proposed as alternatives to mitigate enteric CH4 emissions (EME). Although controlled studies partially support this hypothesis, limited data exists regarding the effectiveness of such strategies when implemented under commercial farm conditions. Therefore, this exploratory case study evaluated farm-level EME and animal performance following the implementation of bundled climate-smart strategies. The study was conducted on a commercial Black Angus cow-calf operation in Westminster, SC. From a 160-head herd, a subset of 29 cows (418±20 kg; 3.5 years old) and 18 calves (200±5.1 kg; 5.5 months old) were randomly assigned to either a control pasture (CON; continuous grazing with inorganic fertilization) or to an adjacent pasture managed under climate-smart practices (CLIM; rotational grazing, organic N fertilization, and overseeding of crimson clover −Trifolium incarnatum−), each comprising 10 ha. Average daily gain (ADG) and forage intake were evaluated, while EME was quantified through the GreenFeed system (C-Lock, Inc.). In addition, ruminal fermentation was evaluated using two independent in-vitro incubations in a completely randomized design. Cows grazing CLIM exhibited greater average ADG (0.4±0.01 vs. 0.3±0.08 kg/d), lower CH4 yield (12.8±0.2 vs. 16.1±0.15 g CH4/ kg of DM intake) and lower intensity (278.5±3.9 vs. 373.2±4.4 g CH4/ kg ADG) when compared to cows grazing CON. Fescue from CLIM had lower neutral acid detergent (NDF; 24% lower) and acid detergent fiber (ADF; 17% lower) but greater crude protein (CP; 20% greater) compared to fescue from CON pasture (P < 0.01). Crimson clover samples exhibited lower NDF and ADF (45% and 25%, respectively), and greater CP and NEm (76% and 87%, respectively) than fescue. In vitro organic matter digestibility was greater in CLIM (69.2 vs. 66.7%; P = 0.04) and in-vitro CH4 yield was reduced (0.56 vs. 1.45 mmol/g organic matter fermented; P < 0.001) when compared to CON. These preliminary findings suggest that implementing climate smart practices at the farm level may improve animal performance while reducing EME intensity in grazing cow-calf operations. Further replicated hypothesis-driven studies in commercial systems are required to confirm these observations.