Wood kraft pulp (KP) is a highly nutritious feed material with potential for mitigating subacute ruminal acidosis (SARA) due to its high digestibility and mild fermentation properties. This study identified the effects of KP feeding on changes in ruminal pH, fermentation, and epithelial transcriptomic dynamics during the 2 weeks of a SARA challenge. Five fistulated Holstein bulls (BW 215 ± 20 kg) were used. Following a 7-d high-forage adaptation, the SARA challenge was conducted for 14 d (d 1–14) and was repeated twice. During the challenge, the control group (n = 5) was fed the SARA challenge diet, and the KP group (n = 5) was fed the same diet, except that half of the flaked corn was replaced with KP (1 kg/day). Ruminal pH was measured continuously. Ruminal volatile fatty acid (VFA) and NH₃-N, and blood metabolites were determined. The rumen epithelium was biopsied on d 14. The mRNA expression profiles were examined by one-color microarray analysis. Differentially expressed genes were analyzed using an Ingenuity pathway analysis. The KP group showed significantly higher levels of acetic acid and blood urea nitrogen, and lower level of blood 3-hydroxybutyrate than did those in the control group. However, no significant differences were observed in ruminal pH, total VFA concentration, or other blood metabolites between the 2 groups. The in silico analysis revealed that the most activated canonical pathway involved PPAR signaling (z-score = 2.83, P = 8.32 × 10⁻⁶), and the immune modulatory Toll-like receptor (z-score = −2.12, P = 8.51 × 10⁻⁴) and NF-κB (z-score = −2.45, P = 1.58 × 10⁻⁴) signaling pathways were significantly inhibited. Furthermore, the genes involved in the immune function (CRK, IgG, MAPK, and NFKB1) and energy metabolism (APOB, INSIG1, and PPARA) were identified as significant upstream regulators based on their expression patterns. The inhibition of immune modulatory and inflammatory signaling pathways in the rumen epithelium suggests milder fermentable properties of the KP diet than those of the flaked corn diet.