In Situ Digestion Kinetics and Ruminal Turnover Rates of Normal and Brown Midrib Mutant Sorghum × Sudangrass Hays Fed to Nonlactating Holstein Cows

Four nonlactating Holstein cows were fed all-forage diets, consisting of two brown midrib mutant sorghum x sudangrass hybrids (Redlan x Greenleaf and Redlan x Piper) and their normal counterparts, to assess the effects of the brown midrib mutation on the rate and extent of in situ cell wall digestion and on ruminal liquid and particulate turnover rates. The four diets were preserved as hay and coarsely chopped prior to feeding in a 4 x 4 Latin square design. Brown midrib genotypes had lower NDF, acid detergent lignin, and hemicellulose concentrations than did normal genotypes. There was no significant difference between brown midrib and normal diets in the rate of in situ cell wall digestion or in digestion lag time. However, brown midrib diets had greater extent of digestion and greater apparent digestibility than normal diets. There was no difference between genotypes in ruminal liquid or particulate turnover rates. In this experiment, lignin concentration had no effect on the rate of in situ digestion or on the rate of ruminal digesta flow.