Disappearance of hemicellulosic monosaccharides and alkali-soluble phenolic compounds of normal and brown midrib sorghum x sudangrasses fed to heifers and sheep.

Eight yearling Holstein heifers (330 kg) were utilized in two 4 x 4 Latin squares. Diets were normal and brown midrib genotypes of Redlan x Greenleaf and Redlan x Piper varieties of ensiled first-cutting sorghum-sudangrass harvested at early head stage of maturity. Composition of hemicellulosic monosaccharides and alkali-soluble lignin phenolic compounds in feeds and corresponding digestibilities were estimated. Arabinose, xylose, and uronic acids were more digestible in brown midrib genotypes than in normal genotypes. p-Coumaric acid disappearance was higher in heifers consuming normal genotypes than in those on brown midrib mutants. In a second experiment, four Suffolk wethers with ruminal, duodenal, and ileal cannulae were utilized in a 4 x 4 Latin square design. Diets were second-cutting sorghum-sudangrass harvested at prehead stage of maturity as baled hay. Digestibilities were determined in the same manner as for heifers. Brown midrib genotypes had higher hemicellulosic monosaccharides, galactose, and uronic acids than did normal genotypes. Xylose content of the brown midrib mutant of Redlan x Piper was higher than that of the corresponding normal genotype. Total tract galactose digestibility was higher in brown midrib genotypes than in normal genotypes. Total tract hemicellulose digestibility (estimated by summing fractional digestibilities of hemicellulosic monosaccharides) was higher in brown midrib mutants than in normal genotypes.