In the Reunion Island, urea-ammonia treatment has been successfully tested as preservative of moist fibrous sugarcane residues (SCR). However, its potential as animal feed has not yet been evaluated. Two feeding trials were conducted at a commercial dairy heifer farm. In experiment 1, 22 heifers (230 kg live weight (LW)) were divided into two groups of 11 heifers. During 45 days, one group was given urea-treated SCR (TSCR) ad libitum plus 1 kg molasses; the second group was given untreated SCR (USCR) ad libitum plus 1 kg molasses-urea mixture (4\% urea). In addition, both groups were also offered 3 kg concentrate plus a mineral and vitamin mixture (daily). The average voluntary dry matter intake (DMI) of roughage for TSCR and USCR were 1.72 and 1.39 kg per 100 kg LW, respectively. Daily weight gain (DWG) for TSCR and USCR was significantly different (896 versus 741 g per day, respectively, P = 0.017). In experiment 2, 40 heifers (255 kg LW) were divided into two groups of 20 heifers. During two 45 days periods, one group was fed TSCR ad libitum plus 0.5 kg molasses per head; the second group was fed USCR ad libitum plus 0.5 kg molasses-urea mixture (4\% urea) per head. Both groups also received a daily 4 kg concentrate plus a mineral and vitamin mixture. In addition, both groups were also offered 1 kg dehydrated lucerne in period 1, which were replaced by 1 kg sugar beet pulp (SBP) in period II. During period I, the DMI in TSCR and USCR were identical to those observed in experiment 1. DWG for TSCR and USCR was not significantly different (700 versus 679 g per day, P = 0.67). In period II, DMI decreased and DWG for TSCR and USCR was significantly different (806 versus 681 g per day, P = 0.006). There was no significant difference (P > 0.05) for the other growth parameters. Plasma urea concentration was significantly higher (P < 0.001) in TSCR than in USCR. It is concluded that urea treatment of SCR increases DMI, but the level of concentrate supplementation may have to be lowered and/or its composition may have to be changed in order to efficiently use such roughage for growing dairy heifers. (C) 2002 Elsevier Science B.V. All rights reserved.