Differential Taurine Profiles Reflect Concentrate‐Driven Physiological Adaptations in Japanese Black Steers During the Middle Fattening Stage

Taurine, a sulfur-containing amino acid derived from methionine or cysteine, plays key roles in bile acid conjugation, antioxidant defense, and lipid and glucose metabolism. However, its relationship with physiological and metabolic changes in Japanese Black cattle, especially during the middle fattening stage, when plasma taurine rises with increased concentrate feeding, remains unclear. This study aimed to clarify the association between plasma taurine concentration and metabolic as well as ruminal characteristics during the middle fattening stage in Japanese Black steers (Bos taurus). Among the 21 steers, the highest (TauH, n = 6) and lowest (TauL, n = 6) steers in plasma taurine concentration were selected for comparison and their growth performance, blood metabolites, and rumen fermentation profiles were compared. The TauH group showed higher concentrate intake, greater ruminal propionate production, superior growth performance, and elevated plasma insulin, cholesterol, phospholipid, and aspartic acid concentrations than the TauL group. KEGG Orthology analysis indicated that methionine biosynthesis was enhanced in the rumen microbiota of TauH steers, whereas cysteine-related pathways predominated in TauL animals. Plasma taurine concentration closely reflected concentrate-driven metabolic adaptation, indicating that it represents a practical biomarker for assessing nutritional status and refining feeding strategies to improve growth and metabolic efficiency in beef cattle.