The objective of this study was to compare the feed intake, digestibility and metabolism in lambs fed low-quality roughage with those of lambs fed normal roughage from an early stage of their life. The study consisted of two treatments [low-quality roughage group (LR) and control group (C)] over three time periods (P1, P2 and P3; 2 months each). Four lambs (4 months old) were allocated to each treatment. In P1 and P2, LR was fed sudangrass hay (CP: 5.1% DM; NDF: 70.4% DM), whereas C was fed timothy hay (CP: 8.4% DM; NDF: 60.3% DM). In P3, all lambs were fed sudangrass hay. Although the feed intake was significantly greater (p < 0.05) in C in P1, there were no differences between the groups in P2. The digestibility, serum glucose (GLU), urea nitrogen (SUN) and insulin-like growth factor 1 (IGF-1) did not differ between the groups in P1 and P2. The average nitrogen retention, triiodothyronine (T3) and thyroxine (T4) were significantly higher in C (p < 0.05) during P1 and P2. No interaction was observed between the treatment and periods. In P3, the feed intake was greater in C (p < 0.05), whereas digestibility and nitrogen retention tended to be greater in LR. The body weight did not differ between the treatments. T4 and T3 were numerically lower in LR, while the SUN was greater in LR (p < 0.05). These results suggest that the early experience with low-quality roughage may have improved feed digestibility and nitrogen metabolism in lambs after 4 months of rearing. Furthermore, the experienced lambs became more efficient at utilizing the low-quality roughage. The lower thyroid hormone concentrations observed in LR suggest an adaptive change occurred in experienced lambs that to a lower basal metabolic rate.