The aim of this study was to evaluate the effect of a commercially available herbal preparation (Oxyphenol (R), I-Green, Padua, Daly) of Pinus taeda hydrolyzed lignin (PTHL) on beef fattening performance, in vitro rumen apparent digestibility, volatile fatty acid (VFA) and gas production. Forty Limousine steers were randomly divided into two groups of twenty individuals each and reared in two separated pens. The control (CON) group did not receive PTHL whereas the experimental group was supplemented with PTHL (35 g/day for each for the first 90 days of the trial and 70 g/day for each for other 30 days). The data set of in vitro rumen apparent digestibility, WA and gas production was subjected to analysis of variance (ANOVA) using the GLM procedure in SAS software (SAS 9.4), considering the dietary treatment and the time as fixed effects. The inclusion of PTHL did not affect slaughter performance, with no differences in live weight at slaughter, daily weight gain and carcass dressing percentage between groups. In addition, the apparent digestibility of nutrients tested (dry matter, organic matter, crude fiber, NDF, crude protein and ether extract) was unaffected both by the dietary treatment and by sampling time. Rumen fluid pH was unaffected both by either dietary treatment or the sampling time, showing mean values ranging from 6.53 to 6.61. The acetate concentration was significantly greater for rumen fluid from PTHL group than in CON one, from 30 to 120 days (P < 0.01). Propionate production showed higher levels in rumen fluid from the PTHL group at 60, 90 and 120 days of supplement administration (P < 0.001). Conversely, butyrate concentrations showed an opposite trend, with lower content in rumen fluid from the PTHL group, compared with CON group at 30 days (P = 0.0188). Total WA concentration did not show significant differences because of sampling time (P > 0.05), but the dietary effect induced higher values in PTHL group from 30 to 120 days (P < 0.05). Finally, rumen fluid from PTHL during fermentation produced less CH4 relative to CON, with lower values from 30 to 120 days compared to day 0 (P < 0.001). Dietary inclusion of PTHL reduced CH4 production but did not affect apparent digestibility and live and slaughter performance.