Insights into Enteric Methane Emissions in Conventional and Organic Dairy Grazing Systems in Island Regions

Pasture-based dairy systems are a cornerstone of agricultural practices in the Azores, contributing significantly to both the local economy and environmental sustainability. However, the environmental impact of these systems, particularly in terms of methane (CH4) emissions, remains a major challenge, especially given the need to balance productivity with ecological preservation. This study aimed to compare enteric methane emissions, floristic composition, productivity, and nutritional quality between conventional and organic pasture systems in the Azores. Data were collected from representative dairy farms over a 12-month period, with pasture samples analyzed monthly to assess floristic diversity, dry matter productivity, and nutritional quality (crude protein and digestibility). Methane emissions were estimated using the IPCC Tier 2 methodology, incorporating data on animal performance, diet composition, and energy intake to calculate CH4 emissions per cow per year. The results showed that organic pastures had greater floristic diversity (5.10 +/- 0.25 species/m2) than conventional pastures (4.00 +/- 0.23 species/m2). However, conventional systems exhibited higher dry matter productivity (22.85 g/m2 vs. 15.35 g/m2) and incorporated corn silage, which enhanced digestible energy and reduced methane emissions (81.33 kg CH4/cow/year) compared to organic systems (89.17 kg CH4/cow/year). Although organic pastures had higher crude protein content (20.65%), their lower digestibility contributed to higher methane emissions. This study underscores the trade-offs between environmental sustainability, pasture productivity, and methane mitigation in pasture-based dairy systems, highlighting the need for integrated management approaches that balance ecological and production goals.