Bioclimatic Influence on the Nutritional Composition, In Vitro Ruminal Fermentation Dynamics, and Greenhouse Gas Emissions of Urtica dioica

Climate change, feed shortages, and rising production costs highlight the need for alternative and sustainable forages for ruminants. This study aimed to evaluate the nutritional composition, in vitro ruminal fermentation, and methane emissions of Urtica dioica ecotypes originating from contrasting bioclimatic zones in Tunisia. Aerial parts of Urtica dioica were harvested at the early flowering stage from arid, semi-arid, and sub-humid regions. Samples were subjected to chemical composition in vitro ruminal fermentation to determine dry matter degradability (DMD), neutral detergent fiber degradability (NDFD), metabolizable energy (ME), and methane production. The results demonstrate that Urtica dioica is a promising protein-rich forage, with a stable crude protein content across ecotypes (18.58–20.97% of dry matter). In contrast, NDFD, DMD, ME, and methane emissions varied significantly according to origin. The arid ecotype, characterized by the highest fiber, ether extract, and polyphenol content, exhibited the lowest DMD (53% vs. 61% and 60%), NDFD (45% vs. 55% and 56%), and ME (7.2 vs. 8.6 and 9.0 MJ/kg dry matter) but produced the lowest methane emissions (38.8 vs. 53.2 and 74.2 mL CH4/kg DMD) compared with the semi-arid and sub-humid ecotypes. The semi-arid and sub-humid ecotypes had comparable DMD, NDFD, and ME values; however, methane emissions were higher in the sub-humid ecotype. Overall, the semi-arid ecotype provided the most favorable balance between nutritive quality and environmental sustainability. These findings highlight the critical role of ecological origin in determining the feeding value and greenhouse gas footprint of Urtica dioica, providing a scientific basis for its potential use as a sustainable forage in ruminant feeding systems.