Grazing Management and Dietary Supplementation Modulate Rumen Fermentation and Methane Production in Forage‐Based Livestock Systems

ABSTRACT Assessing the effectiveness of grazing management and anti‐methanogenic dietary supplements on tropical pastures is crucial for sustainable livestock production and methane (CH 4 ) mitigation. This study aimed to: (1) compare forage mass, plant part composition, and nutritive value of ‘Mulato II’ hybrid brachiariagrass ( Urochloa spp.) managed under continuous (C) or rotational stocking with lenient (RL) or moderate (RM) defoliation at 20 and 30 cm; and (2) evaluate the effects of these strategies combined with supplementation (Control, Nitrate + elemental sulfur [NS], soybean oil [SO], corn bran [CB], and SO + CB) on fermentation kinetics and CH 4 production. The C20 and RL20 treatments showed superior nutritive value—631 g kg −1 of neutral detergent fibre (NDF), 144 g kg −1 of crude protein (CP), and 591 g kg −1 of NDF degradability (NDFd)—and the highest Partition Factor (PF), but produced more CH 4 (6.3 mL g −1 dNDF). Conversely, RM30 forage had greater NDF (662 g kg −1 DM), less CP (100 g kg −1 DM), and lower NDFd (550 g kg −1 ), resulting in the least methane production (5.5 mL g −1 dNDF). All supplementations reduced CH 4 compared to the control. Additive effects in SO + CB increased NDFd (614 g kg −1 ) and reduced CH 4 by 29.5% without affecting ammonia nitrogen (NH 3 –N). NS had greater NH 3 –N (54 mg dL −1 ) and reduced CH 4 by 93.2% but decreased NDFd (505 g kg −1 ). Optimising forage quality (C20 and RL20) combined with NS or SO + CB provides the best integrated mitigation strategy.