Greenhouse gases, nutrition, rumen fermentation, and microbiome of lambs fed sugarcane silage versus sugarcane/Moringa oleifera

Silage is widely used in tropical ruminant systems, although the low crude protein content of some conserved forages may limit nutrient supply and ruminal function. This study evaluated the effects of partially replacing sugarcane silage with Moringa oleifera silage on feed intake, physiological responses, rumen microbial abundance, and greenhouse gas emissions in lambs. Sixteen Santa Inês × Dorper lambs were assigned to two dietary treatments: sugarcane silage (C) or sugarcane silage partially replaced with M. oleifera silage (C+M; 50:50 on a dry matter basis). Feed intake dynamics, serum biochemical parameters, infrared thermography, rumen microbial abundance assessed by qPCR, and gaseous emissions (CH₄, CO₂, N₂O, and NH₃) measured in respiration chambers were evaluated. The C+M diet increased dietary crude protein without markedly changing fiber fractions and was associated with a more stable intake pattern over time. Physiological indicators remained within normal reference ranges, suggesting no evidence of systemic metabolic stress. Methane and nitrous oxide emissions were not affected by dietary treatment (P > 0.05), whereas carbon dioxide and ammonia emissions were higher in lambs fed the C+M diet (CO₂: 173.82 vs. 88.36 g/kg DMI, P = 0.039; NH₃: 1.35 vs. 0.31 g/kg DMI, P = 0.022). Fungal abundance was lower under the C+M diet (P = 0.016), while total bacterial abundance remained unchanged and protozoal populations declined over time in both treatments. Overall, partial replacement of sugarcane silage with M. oleifera improved the dietary protein profile and was associated with changes in intake dynamics, selected rumen microbial groups, and emission profiles, without reducing methane emissions under the conditions of the present study. These findings suggest that M. oleifera may be a promising forage resource for tropical sheep production systems, although further studies are needed to clarify the mechanisms involved and optimize inclusion levels.