Dietary plant extracts reduce methane emission and modulate rumen microbial functionality in Merino lambs

The formation of enteric methane from ruminants represents a significant loss of dietary energy that adversely affects growth and production while also contributing to the environmental footprint of livestock production through greenhouse gas accumulation. Phytogenic feed additives rich in bioactive compounds have been proposed as sustainable alternatives to synthetic additives for improving nutrient utilisation and reducing methane. This study evaluated the effects of Moringa oleifera, Jatropha curcas, and Aloe vera extracts on growth performance, nutrient digestibility, methane production, rumen fermentation in South African Mutton Merino lambs using an in vivo feeding trial while the microbial diversity and functionality was evaluated using shotgun metagenomic sequencing. Supplementation with Moringa and Jatropha improved dry matter and crude protein digestibility (P < 0.05). Methane emission decreased in all plant extract groups, with reductions of 17% (Jatropha), 9% (Moringa), and 12% (Aloe) relative to control (P < 0.05). Ammonia nitrogen concentrations were lower in supplemented groups, particularly Moringa and Aloe (P < 0.01), while volatile fatty acids and growth performance were unaffected. Metagenomic profiling revealed Bacteroidetes as the dominant phylum and showed enrichment of genes which may be associated with protein biosynthesis and carbohydrate metabolism in Moringa and Jatropha lambs, aligning with improved digestibility and reduced methane emissions. Dietary inclusion of M. oleifera, J. curcas, and A. vera extracts reduced methane emissions and improved dry matter and crude protein digestibility without compromising growth. These results suggest that these phytogenic extracts can serve as sustainable feed additives to improve efficiency and mitigate environmental impacts in ruminant production systems.