An Integrated Life Cycle Assessment and Mathematical Modeling Framework for Quantifying Enteric Methane Emissions from Philippine Buffalo (Bubalus bubalis carabanensis) Heifers

Enteric methane (CH₄) emissions from ruminants are a significant contributor to agricultural greenhouse gases, necessitating reliable estimation methods to support climate change mitigation strategies. This study developed an integrated Life Cycle Assessment (LCA)-based framework to quantify enteric CH₄ emissions from Philippine buffalo (Bubalus bubalis carabanensis) heifers fed with Mombasa grass and rice straw. Feed composition was experimentally determined and incorporated into established methane estimation models, Aspen Plus V8.8 process simulation, and a newly developed mathematical model specific to Philippine feeding conditions. Existing models predicted CH₄ emissions ranging from 0.1964 to 0.8164 kg head⁻¹ day⁻¹, whereas the developed model estimated 0.0642 kg head⁻¹ day⁻¹ (23.44 kg head⁻¹ year⁻¹), demonstrating a substantially lower estimate attributable to locally derived feed characteristics and model assumptions. Statistical analysis indicated no significant differences in CH₄ emissions among individual heifers, although daily emissions varied significantly throughout the feeding trial. The developed predictive equation, based on glucose, crude protein, neutral detergent fiber, crude fat, ash, and water content, achieved an average absolute percentage deviation of 0.7448%, indicating excellent model fit. The findings further confirmed that methane production increases with feed intake and is strongly influenced by forage quality. The proposed framework provides a practical baseline for evaluating feeding strategies and supporting greenhouse gas mitigation in Philippine buffalo production systems.