An experiment was conducted to (i) determine the effect of heat treatment and thermal ammoniation on dry-matter digestibility and true metabolizable energy content of high-tannin grain sorghum in a digestion trial with roosters and (ii) to determine the relative nutritive value of the different test components in a slope ratio assay with rats. Thermal ammoniation reduced the tannin content of high-tannin grain sorghum by 55,1% whereas heat treatment per se had no effect. Dry-matter digestibility and true metabolizable energy content were significantly (P ≤ 0,01) improved by 4,7 and 8,9% by thermal ammoniation, respectively. In the slope ratio assay with rats, no significant differences were obtained in the relative nutritive value of the test components.