Straw is a major by-product of the grain industry. Indirect ammoniation by urea to improve the nutritive value of straw was investigated. Ammoniated and untreated wheat straw were compared in a 2 x 2 factorial experiment at CP levels of 9 and 13%, using 20 adult SA Mutton Merino wethers. Ammoniation improved voluntary intake and the apparent digestibility of OM significantly, by 27,3% (P ≤0,01) and 7,1% (P ≤0,05) respectively, resulting in a marked increase of 36,3% in DOM intake per W0.75. The apparent digestibility of CF, CWC and hemicellulose were also significantly (P ≤0,01) improved by ammoniation. The improvement in the apparent digestibility of ADF was not significant. CP level did not affect voluntary DM intake, but at the higher CP level apparent digestibility of OM, CF, ADF, CWC and hemicellulose were improved by 6,2; 6,5; 4,7; 5,4 and 4,1% respectively. This trend reached significance (P ≤0,05) only in the case of OM and CF. N-retention and the apparent digestibility of CP were significantly (P ≤0,01) reduced by ammoniation. Because of the higher intakes obtained on the ammoniated diets DCP intake per W0.75 was unaffected. N-retention and the apparent digestibility of CP were significantly (P ≤0,01) improved at the higher CP level. Despite the reduction in CP digestibility and N-retention, ammoniation by urea seems to be a practical way to improve the nutritive value of low quality roughages.