Eight growing Holstein heifers and four ruminally cannulated adult Holstein steers fed ad libitum were used in 4 X 4 Latin square designs. Diets included two sorghum X sudangrass varieties, Redlan X Greenleaf and Redlan X Piper, and their corresponding brown midrib mutants. Acid detergent fiber and acid detergent lignin concentrations tended to be lower for brown midrib mutants than for normal genotypes of the same variety. Digestion kinetics for in situ studies showed no difference in rate constants between normal and brown midrib sorghums, but extent of digestion at 72 h was significantly higher for brown midrib mutants than for normal genotypes, suggesting that lignin has no effect on digestion rate but does result in a decreased extent of digestion. In growing dairy heifers, brown midrib sorghum X sudangrass had higher digestibilities for organic matter, neutral detergent fiber, acid detergent fiber, cellulose, and hemicellulose fractions than did the normal genotype for Redlan X Greenleaf.
The objectives of this experiment were to determine fluid and particulate rate of passage from the rumen and extent of digestion at various sites along the gastrointestinal tract in sheep fed normal and brown midrib sorghum X sudangrass hybrids. Four Suffolk wethers (80 kg) with ruminal, duodenal and ileal cannulae were assigned to one of four diets in a 4 X 4 Latin square with a 2 X 2 factorial arrangement of treatments. Diets were hays of two sorghum X sudangrass varieties, Redlan X Greenleaf and Redlan X Piper, and their corresponding brown midrib mutants. There were no compositional differences resulting from variety or genotype in lignin content or fiber components, although alkali-soluble phenolic acids were higher in normal genotypes than in brown midrib. Vanillin was lower, whereas para-coumaric acid was higher, in normal genotypes than in brown midrib mutants. Ruminal digestibility of neutral detergent fiber, acid detergent fiber and cellulose was lower (P less than .05) for normal genotypes than for the brown midribs. Total-tract digestibility of cellulose was higher (P less than .05) for brown midrib mutants than for corresponding normal genotypes. No quantitative differences in fiber composition or lignin content were detected between normal and brown midrib genotypes; however, differences in composition of alkali-soluble phenolic acids of the lignin fraction could explain differences in digestibility detected between the two genotypes.
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.
Four ruminally cannulated Holstein steers fed ad libitum were used in a 4 x 4 Latin square design. Feeds were normal and brown midrib genotypes of Redlan x Piper and Redlan x Greenleaf sorghum-sudangrasses. An in situ trial was run in conjunction with the digestibility trial as part of the data collection for each period. Hemicellulosic monosaccharide and alkali-soluble lignin phenolic compound disappearances were quantitated. The xylose to arabinose ratio was higher in normal genotypes than in brown midribs. Normal genotypes had higher concentrations of alkali-soluble p-coumaric acid and lower vanillin, vanillic acid, and sinapic acid than did brown midrib mutants. Disappearance of p-coumaric acid was higher in steers consuming normal genotypes than in those consuming brown midribs. Neutral detergent fiber, acid detergent fiber, hemicellulose, cellulose, and acid detergent lignin showed no genotypic differences in rate of digestion, but extent of 72 h digestion was higher for brown midrib mutants than for normal genotypes. Extent of digestion of the hemicellulosic monosaccharides, xylose, and uronic acids was higher in situ for brown midrib silages compared with normal genotypes. Differences in alkali-soluble phenolic compound and cell wall monosaccharide profiles between normal and brown midrib genotypes may help explain digestibility differences between the two genotypes.
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