Chemically Treated Alfalfa: Lignin Composition and In Situ Disappearance of Neutral Detergent Fiber Components

¹ Ruminant Nutrition Laboratory, Livestock and Poultry Sciences Institute, Agricultural Research Service, USDA, Beltsville, MD 20705

The effect or effects of varying levels of alkali (NaOH) or oxidant (NaClO₂) on composition of alfalfa and in situ disappearance of OM, NDF, and NDF monosaccharides were determined. Three field replicates of fourth-cutting alfalfa (early and late bud) were treated at harvest with 0, 2, 4, 6, or 8 g of NaOH or NaClO₂/100 g of herbage DM. Herbage was hand cut (15-cm stubble height), hand sprayed, and artificially dried (50°C). Alkali treatment linearly increased NDF, crude hemicellulose, and NDF N but decreased CP. Quantity or composition of lignin was not altered consistently by NaOH treatment. Glucose concentration was lowered as a result of NaOH treatment. Oxidant linearly decreased NDF, lignin, ADF N, CP, and concentration of lignin nitrobenzene oxidation products. Alkali and oxidant treatment linearly increased in situ disappearance of OM and NDR NaOH tended to increase xylose disappearance, whereas NaClO₂ tended to increase glucose disappearance. Both treatments increased arabinose disappearance. Alkali and oxidant had divergent effects on fiber and lignin composition, yet both types of treatment increased potential disappearance of NDF. Disappearance of NDF in chemically treated alfalfa may not be related to quantity or composition of lignin.

Key Words: alfalfa • lignin • neutral detergent fiber

Submitted on December 12, 1991
Accepted on February 21, 1992