The aim of this experiment was to test the effectiveness of two diets in increasing liveweight (LW) and body condition score (BCS) of Brahman cows in Indonesia. Diets were based on rice straw, with additional energy and nitrogen (N) provided in the form of onggok (a cassava by-product) plus urea or a tree legume. Thirty mature, non-pregnant, non-lactating Brahman crossbred cows (288 kg LW, BCS 2/5) were allocated to one of two treatment groups. Cows were kept in individual pens for 21 weeks and offered one of two diets; (1) urea-supplemented rice straw ad libitum plus 10 g onggok DM/kg LW.day, or (2) untreated rice straw ad libitum plus 5 g onggok DM/kg LW.day and 5 g Gliricidia sepium DM/kg LW.day. The urea supplement provided no advantages over using locally available N sources such as gliricidia, with both supplement types meeting the rumen-degradable N requirements of the cows. Cows on both diets gained weight at a similar rate (0.19 kg/day) for the first 15 weeks of the experiment. Liveweight gain in Weeks 16–21 was only 0.04 kg/day, despite an increase in total feed intake and energy content of the diets compared with Weeks 1–15. Liveweight of cows stabilised during Weeks 16–21 at 304 kg, BCS 2.2. While our results demonstrate that Brahman cows can maintain LW on rice straw-based diets, they may not be able to maintain a BCS sufficient for good reproduction rates (i.e. BCS 3 or higher on 1–5 scale). Better quality diets containing higher levels of energy are required for cows to gain and maintain a suitable BCS.