Effects of Neolamarckia cadamba leaves extract on methanogenesis, microbial community in the rumen and digestibility of stylo silage

Methane emission from the ruminants is not only a significant amount of greenhouse gases contributing to climate change but also a reduction in feed efficacy. Mitigation of ruminal CH₄ emission is a great challenge for cleaner livestock production. It is difficult to reduce CH₄ production without any adverse effects on feed digestion. The present investigation was conducted to explore the sustainable mitigation of ruminal CH₄ production with positive effects on feed digestibility using Neolamarckia cadamba leaves extract (NE). Stylo was added and ensiled with or without 1% and 2% NE, and the silage was engaged in vitro ruminal fermentation. Metagenomics was used to analyze the microbial communities and functional genes. The results indicated that the addition of 1% and 2% NE decreased (P < 0.001) CH₄ production significantly and increased (P < 0.001) dry matter digestibility at the same time. The concentrations of volatile fatty acids were not altered by NE. Some genes related to glycoside hydrolases, glycosyl transferases, carbohydrate-binding modules were upregulated by 2%NE. The addition of NE showed little influence on the ruminal microbial community, but reduced (P < 0.05) the relative abundance of Methanobrevibacter, especially the Methanobrevibacter curvatus, which was positively correlated (correlation = 0.561, P = 0.011) with the ruminal CH₄ production. In CH₄ metabolism, genes related to the serine pathway were highly detected. The addition of NE inhibited (P < 0.05) CH₄ metabolism by downregulating the great majority of involved genes. In conclusion, the present study provides new insights into the pathway of CH₄ metabolism and useful information for understanding and controlling ruminal CH₄ production in livestock production. The addition of NE might be a sustainable option to reduce CH₄ while enhancing animal feed utilization efficiency. It could be used as a pronounced cleaner way for the ecosystem as well as livestock.