STUDIES ON THE CHEMICAL-COMPOSITION AND DIGESTIBLE ENERGY CONTENT OF SOUTH-AFRICAN GRAIN-SORGHUM

The experiment was conducted (i) to compare the chemical and physical composition of grain sorghum produced at different locations, (ii) to compare the digestible energy (DE) content of different grain sorghum cultivars produced at different locations, and (iii) to evaluate the influence of chemical composition and physical characteristics of the grain on the DE contents thereof. Highly significant (P less-than-or-equal-to 0.01) differences in crude protein (CP), crude fibre (CF), tannin and starch content as well as in hectolitre and thousand seed mass, DM digestibility and DE content were observed between sorghum produced at different locations. Significant (P less-than-or-equal-to 0.01) differences were also found between the DE content of different grain sorghum cultivars, while significant (P less-than-or-equal-to 0.01) interactions were found between location and cultivar. The mean DE content for low tannin (GL) sorghum cultivars was determined to be 16.1 +/- 0.6 MJ/kg DM, while the corresponding value for high tannin (GH) sorghum cultivars was 14.1 +/- 0.6 MJ/kg DM. The mean DE contents for GL cultivars were 16.7 +/- 1.2 and 16.1 +/- 1.2 MJ/kg DM in the Bethlehem and Ermelo locations respectively, while the DE contents for GH cultivars were 15.0 +/- 0.9 and 13.5 +/- 1.9 MJ/kg DM respectively. Concerning the influence of physical parameters on DE, it was found that the percentage small seeds (< 2 mm) and percentage unthreshed grain had a negative influence on DE content. Tannin content affected DE negatively (significant at P less-than-or-equal-to 0.01), while starch and protein content influenced DE positively (significant at P less-than-or-equal-to 0.01). It was concluded from the study that the South African grain sorghum grading system accounts for the differences in DE content through the amounts of unthreshed grain and small seeds allowed in each grade.