Brown Midrib Sorghum Research Articles

Digestion Kinetics and Composition of Normal and Brown Midrib Sorghum Morphological Components

The brown midrib (bmr) mutation has shown the potential to improve the nutritive quality of forage sorghum [Sorghum bicolor (L.) Moench]; however, no study has been conducted to directly compare the effect of the bmr gene in a sudangrass (sorghum × drummondii (Steudel) Millsp. & Chase) and its hybrid with a grain sorghum. Research was conducted to evaluate the relationship between cell wall composition and digestibility within the morphological components of normal and bmr sorghum cultivars. Cell wall constituents, structural carbohydrates, alkali‐labile phenolic monomers, and in vitro digestion kinetics were determined for ‘Piper’ (normal sudangrass), ‘S407’ (Piper. bmr‐6 sudangrass), and ‘F1006‐8 × S407’ (male sterile grain type bmr‐6 sorghum × Piper bmr‐6 sudangrass). Whole plants were harvested at the boot and hard dough growth stages and separated in to leaf blade, leaf sheath, inflorescence, and stem components. Significant differences were found between cultivars in concentrations of cell wall constituents. Neutral detergent fiber (NDF) concentration was lower (P < 0.05) in the bmr cultivars than in Piper due to lower concentrations of cellulose and acid detergent lignin (ADL). Concentrations of ADL averaged g kg−1 dry matter for Piper, 28 g kg−1 for S407, and 25 g kg−1 for F1006‐8 × S407. The bmr cultivars had lower (P<0.05) concentrations of p‐coumaric acid and higher (P < 0.05) concentrations of vanillin than Piper. There were no differences (P > 0.05) among cultivars ferulic acid concentration. p‐Coumaric acid concentrations averaged 25 g kg−1 of NDF for Piper, 16 g kg−1 NDF for S407, and 14 g kg−1 NDF for F1006‐8 − S407. Rate constants for in vitro digestion of NDF were similar (P > 0.05) among cultivars. The bmr sudangrass (S407) had a greater (P < 0.05) extent of NDF digestion than either Piper of F1006‐8 × S407. Extent of NDF digestion averaged 0.596 for Piper, 0.623 for S407, and 0.597 for F1006‐8 × S407. Results of this study indicate that the bmr mutation can effectively be expressed in both sudangrass and sorghum × sudangrass hybrid backgrounds

Disappearance of Hemicellulosic Monosaccharides and Alkali-Soluble Phenolic Compounds of Normal and Brown Midrib Sorghum × Sudangrass Silages Fed to Holstein Steers

Four ruminally cannulated Holstein steers fed ad libitum were used in a 4×4 Latin square design. Feeds were normal and brown midrib genotypes of Redlan×Piper and Redlan×Greenleaf sorghum-sudangrasses. An in situ trial was run in conjuction 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 72h 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.

Disappearance of Hemicellulosic Monosaccharides and Alkali-Soluble Phenolic Compounds of Normal and Brown Midrib Sorghum × Sudangrasses Fed to Heifers and Sheep

Eight yearling Holstein heifers (330kg) were utilized in two 4×4 Latin squares. Diets were normal and brown midrib genotypes of Redlan×Greenleaf and Redlan×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 4×4 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×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.

Effect of brown midrib and normal genotypes of sorghum X sudangrass on ruminal fluid and particulate rate of passage from the rumen and extent of digestion at various sites along the gastrointestinal tract in sheep.

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.

Rumen Turnover and Digestion of Normal and Brown Midrib Sorghum × Sudangrass Hybrid Silages in Dairy Cattle

Eight growing Holstein heifers and four ruminally cannulated adult Holstein steers fed ad libitum were used in 4 × 4 Latin square designs. Diets included two sorghum × sudangrass varieties, Redlan × Greenleaf and Redlan × 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 72h 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 × sudangrass had higher digestibilities for organic matter, neutral detergent fiber, acid detergent fiber, cellulose, and hemicellulose fractions than did the normal genotype for Redlan × Greenleaf.

Brown Midrib Sorghum or Corn Silage for Milk Production

In two total collection digestion experiments and two milk production experiments feeding value of brown midrib sorghum silage (brm 12) was compared with corn silage. Normal sorghum (N12) also was included in the first digestion experiment. Heifers consumed more dry matter from brown midrib sorghum (2.64 versus 1.83 and 2.00 versus 1.68 kg/100kg body weight) than from corn silage for the digestion experiments. No differences were significant for dry matter digestibility between the two silages in either experiment. Protein digestion for corn silage exceeded that for brown midrib sorghum in Experiment 1 (38.3 versus 31.3%); however, this was reversed in Experiment 2 (31.0 versus 41.2%). In Experiment 1, dry matter digestibility (53.3 versus 61.4%) was lowered for normal sorghum compared to corn silage. A 24% (4.4 versus 5.8%) reduction of lignin was obtained from brown midrib sorghum to normal sorghum. The lignin percentage of brown midrib sorghum and corn silages were relatively close in all experiments.No differences were significant for actual milk production, fat-corrected milk production, milk fat percent, protein percent, or flavor scores of milk produced by cows fed corn and brown midrib silages in either milk production experiment.

Brown Midrib Mutants in Sudangrass and Grain Sorghum1

Three low lignin, brown midrib (bmr) sorghum (Sorghum bicolor L. Moench) mutants, designated bmr‐6, bmr‐12, and bmr‐18, were each backcrossed to normal grain‐ and grassy‐type sorghums. The objective was to determine if the effect of the brown midrib mutants on fiber composition would be expressed equally in both grain‐ and grassy‐type genetic backgrounds.Analysis for fiber composition and in vitro dry matter disappearance (IVDMD) was conducted on mature stem tissue of mutant and normal plants from the F2 generation Of the first and second backcross. The bmr‐6 mutant reduced lignin percentage from 10.3 to 8.5 (P < 0.01) and increased IVDMD percentage from 39.6 to 48.7 (P < 0.01). Mutant ✕ background and mutant backcross interactions were not significant (P > 0.10), indicating that the effect of the bmr‐6 mutant was expressed as well in grassy‐type as in grain‐type backgrounds. Similar results were obtained with the bmr‐12 and bmr‐18 mutants. These mutants, evaluated after only one backcross, reduced stem lignin from 8.3 to 6.1% (P < 0.01) and increased IVDMD from 44.0 to 55.5% (P < 0.01). The effects were expressed as well in grassy‐type as in grain‐type backgrounds.Results indicate that sudangrass sorghums containing brown midrib mutant genes are lower in lignin percentage and higher in digestibility than normal genotypes. Mutant sudangrasses of this nature should be higher in digestible energy percentage and should result in greater animal production than normal sudangrasses [Sorghum sudanense (Piper) Stapf] when fed to ruminant animals.