Tree Legumes Forage as a Source of Tannin: Potential Influence on Enteric Methane Mitigation and Rumen Fermentation

Nutritional strategies for reducing greenhouse gases that negatively impact climate change have been investigated in recent years. Secondary compounds such as tannins are found in tree legumes, which have forage potential and the ability to reduce enteric methane emissions. The aim of this research is to evaluate the effect of forage legumes as a tannin source on enteric methane mitigation and rumen fermentation. The species studied were Acacia dealbata, Acacia melanoxylon, Albizzia lophantha, Lupinus pubescens, Inga insignis, Senna multiglandulosa, and Tecoma stans. The range of crude protein content in all species was variable. The neutral detergent fiber content was much higher in I. insignes, while S. multiglandulosa and L. pubescens had a lower content of acid detergent fiber and lignin detergent acid. I. insignes presented a statistically different lower gas production when compared with the other species subjected to in vitro fermentation. The species that presented the greatest potential for the reduction in enteric methane produced were I. insignes and A. melanoxylon. Additionally, a significant variation was evidenced in the pH of the inocula at 24 h of fermentation in a range of 6.82–7.25. S. multiglandulosa presented concentrations for acetate, propionate, and butyrate that differed significantly compared to the other species. Similarly, the highest concentration of NH3-N was for S. multiglandulosa. However, the highest EDDM4% and IVDDM were for I. insignes with 381.28 and 791.46 g/kg, respectively. it can be concluded that forages (e.g., I. insignes) with a higher content of condensed tannins favor rumen digestion and fermentation, probably increasing microbial protein synthesis and thereby reducing ruminal gas and methane production.