The purpose of this study was to use the in vitro gas production (IVGP) method to assess the relative feeding value, feed quality, and anti- methanogenic capabilities of tree leaves added to Italian ryegrass forage at various proportions. With the addition of 2% and 4% willow leaf (Salix alba), 2% and 4% vine leaf (Vitis vinifera), 2% and 4% plane leaf (Platanus orientalis), and a control group devoid of these supplements, a total of 21 forage samples were created. The data were subjected to analysis of variance after nutritional composition, energy content, feeding value, and feed quality were determined using the in vitro gas generation method. The effect of the addition of tree leaves to forage on crude ash, IVGP, methane, metabolizable energy, net energy lactation, organic matter digestion, true digestible dry matter, partitioning factor, microbial protein, microbial protein synthesising efficiency, degree of true digestion, NDF digestion, total digestible nutrients, and relative feed quality was substantial. With the addition of 2% willow leaves, the digestibility, metabolic energy, net energy lactation value, organic matter digestion, microbial protein value, and relative feed quality all improved. The findings showed that tree leaves can be utilized as an alternate feed source for ruminants. Tannin content should be taken into account when preparing rations utilizing tannin-containing tree leaves.