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

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