Ph.D Candidate of Ruminant Nutrition Significance and Impact of the Study: Different metabolic pathways by gastrointestinal microbiota have been suggested for gastrointestinal hydrolysable tannin (HT) metabolism. We argue that complete biotransformation and fermentation of HT metabolites especially pyrogallol to volatile fatty acids is a unique and evolutionary microbial process and have to be examined separately. Exploring the fate of HT metabolites derived from gastrointestinal microbial HT metabolism in whole animal needs to be closely examined in studies that focuses on application of HT ingredients and its effects on ruminant animal performance. We highlight that making inference based on studies that focused on feeding HT ingredients in ruminant nutrition without considering the fate of HT metabolites; will path a strand of literature that may be questionable. Therefore, the future research should consider the fate of HT metabolites to have a reliable result inference.