Abstract Rice straws were either treated with urea (50 g urea in 600 ml of water) and stored for 2 weeks or sprayed with urea solution (20 g urea in 600 ml of water kg −1 DM straw) and fed immediately. These two basal diets were supplemented with rice bran (RB), mineral and vitamin premix, common salt, with or without fish meal (FM) to form four treatment diets. In situ degradability studies and chemical analyses were used to test the effectiveness of urea treatment or supplementation in a completely randomized design using three fistulated sheep fed a standard diet. Animal response when fed urea-treated rice straw (UTRS) or urea-supplemented rice straw (USRS), supplemented with RB with or without FM, was studied using 32 growing female dairy goats in a completely randomized design. Growth rate and dry matter intake (DMI) were recorded for 90 days. The results showed that N content increased from 7.0 (untreated rice straw (URS)) to 17.4 and 18.6 g N kg −1 DM for USRS and UTRS, respectively. The rate of DM degradation was significantly ( P < 0.01) increased from 1.9% (URS) and 3.5% (USRS) to 4.5% h −1 (UTRS). The 48 h DM degradability was improved from 42.5% (URS) and 55.1% (USRS) to 65.7% (UTRS). The effective degradability (ED) calculated assuming passage rates of 2% h −1 and 4% h −1, respectively, were 39.6% and 31.3% (URS), 45.3% and 37.3% (USRS) and 53.6% and 44.1% (UTRS). Urea treatment increased daily straw DMI to 59.3 g kg −1W 0.75 compared with 23.1 g for USRS. This corresponds to 2.9% and 1.2% of body weight, respectively. The total DMI was increased from 45.8 (2.3% of body weight) to 89.4 (4.3% of body weight) g kg −1W 0.75 day −1 for USRS and UTRS based diets, respectively. Both urea treatment and FM supplementation significantly ( P < 0.001) increased average daily gain (ADG) from 3.3 ± 1.5 (USRS) to 36.9 ± 1.5 g day −1 (UTRS) and from 13.0 ± 1.5 g day −1 (USRS + FM) to 49.1 ± 1.5 g day −1 (UTRS + FM). It was concluded that urea treatment promoted DMI with a corresponding increased growth performance by goats due to increased rate and extent of degradation of UTRS compared with USRS. Similarly, when a small amount of FM was supplemented increased weight gains and feed efficiency were observed on both USRS and UTRS based diets.